Here's my new idea (not so new, just not shared around a lot). The general system of age advancement is stolen from Mythos_Ruler's Greek game outline, so props to him. This is basically set in Italy from 1450-1800, during the Renaissance. Hence, Age of Empires 3: Age of Renaissance. Basically, you get to build your own city-state up from the ground. Warning: It's a loooong read. To clear up some things that might be confusing in this:

Age Advancement and Age Choices

Whenever you advance to each of the 4 ages, you don't pick a minor god. Instead you pick and Age Choice. You choose a patron city-state (Chosen before the game starts, equivalent to your civ) (Gunpowder Age), government style (Humanist Age), cultural style (Reformation Age), and foreign ally (Imperial Age). These affect your bonuses and the units you can build. Each patron city-state cannot choose 1 Age Choice per age. For example, Rome cannot choose Democracy government style.

Auxiliaries and Militia

Auxiliaries are only buildable in the Auxiliary Center, and only in the Imperial Age (Except Florence, who can build them every age). Auxiliaries are units "borrowed" from other nations. Each patron city-state has their own unique auxiliary (Florence has 2), and each foreign ally gives you another 2 to build. Auxiliaries build instantly and are very strong, but they are expensive (although they only cost gold) and take up a lot of population.

Militia are a little like Auxiliaries. They are only buildable by Florence (Don't worry, I know Florence sounds OP so far but they're not). Florence can build them from the Town Center. They train instantly, but leave the army in 60 seconds. Villagers can also be turned into militia for a price, and when a Florentine building is destroyed, it leaves Militia in the remnants.

Villager and Army Happiness

Villager Happiness refers to how happy your peasants are. If their happiness is EXTREMELY high, they get a gathering and building bonus. But if it gets too low, they will refuse to work until you raise it up again. Some Age Choices will raise your Villager Happiness, but some Age Choices will lower it, it will also lower if there are enemy units in the vicinity

Army Happiness is a little like Villager Happiness. If it is extremely high, they receive an attack bonus. If it gets too low, they will fight worse, or maybe even abandon you! Some Age Choices will raise it, and some will lower it.

Units through the Ages
Veering off from AoE-land and more into EDotMW-land, your units do not get upgraded from medium to heavy to champion or anything like that. Instead, all the units are independent of each other. For example, if I build an Arquebusier in Gunpowder Age, my general ranged infantry, and then I advance to Humanist Age, my Arquebusier does not automatically upgrade. Instead, my best basic ranged infantry is a Fusilier. I can still build Arquebusier, which is not totally stupid, because it is cheaper than Fusiliers, if weaker. All units, except a few exceptions, are buildable for 2 ages.

Random Unit Notes
Pastors, Priests, Bishops, and Cardinals: Pastors and Priests can heal and convert. However, improved priests, Bishops (Ecclesiasm government style required) and Cardinals (Rome patron city-state required). Bishops are like priests, but have more HP, and heal and convert faster. Cardinals are a little stronger than bishops, and can also empower buildings to work faster. There is a cap of 3 Cardinals.

Petard: Explodes when it attacks. Thus, only usable once.

Boarding Ship and Plated Boarding Ship: Units on it fire arrows at the other ship. However, if the other ship is at 90% or lower health, it can board the ship and convert it to your side (it will probably need to be repaired however).

Condottieri and Corporals: Condottieri (Florence patron only) and Corporals (Militaristic cultural style only) both give attack and speed bonuses to units around them.

Final Notes
Each patron does not have its own units. They all share units like in the original 2 Age games. However, each patron DOES receive at least 5 unique units. Also, each Age Choice will veer you off from other cultures even more. They also each have a handful of bonuses.

Whenever I refer to something like "Army cheaper", I do not mean the whole army. I didn't want to spend all too much time on the bonuses, so I meant one part of the army, undefined. All the resource bonuses are changeable too. I will probably work more on bonuses later.

So now the outline.

Age of Empires 3: Age of Renaissance

Ages: Gunpowder Age, Humanist Age, Reformation Age, Imperial Age
Gunpowder Age: Choose your Patron City State

Venice: Faster villagers, Lower Villager Happiness, buildings have more HP, boats better, trade generates more gold/Cannot choose Monarchy government style, Economic cultural style, or Holy Roman foreign ally/Unique Units: Auxiliary Roundshier (Imperial), Galleass (Imperial), Bombardiere (Reformation/Imperial), Morisini Halberdier (Reformation/Imperial), Morisini Musketeer (Reformation/Imperial)

Florence: Gold mined fasted, trade generates more gold, higher Villager Happiness, lower Army Happiness, buildings cost more, army costs more, can buy Auxiliaries in Gunpowder-Imperial/Cannot choose Ecclesiasm government style, Militaristic cultural style, or Spanish foreign ally/Unique units: Auxiliary Chevalier (Gunpowder/Humanist), Auxiliary Cavalry (Humanist/Reformation), Condottieri (Reformation/Imperial), Militia Arquebusier (Gunpowder/Humanist), Militia Musketeer (Reformation/Imperial), Militia Pikeman (Gunpowder/Humanist), Militia Halberdier (Reformation/Imperial)

Rome: Receives trickle of gold, higher Villager Happiness, higher Army Happiness, technologies cost more, buildings cost more, technologies take longer to research/Cannot choose Democracy government style, Economic cultural style, or English foreign ally/Unique units: Swiss Guard (Humanist/Reformation), Auxiliary Jager (Imperial), Holy Knight (Gunpowder/Humanist), Cardinal (Reformation/Imperial), Papal Guard (Humanist/Reformation)

Naples: Farms faster, higher Army Happiness, buildings cheaper, armies cheaper, armies train slower, boats worse, buildings weaker/Cannot choose Aristocracy government style, Artistic cultural style, or French foreign ally/Unique units: Scutari (Gunpowder/Humanist), Sicilian Gunner (Humanist/Reformation), Reiter (Humanist/Reformation), Auxiliary Lancer (Imperial), Ballista (Gunpowder/Humanist), Privateer (Reformation/Imperial)

Genoa: Trade generates more gold, wood gathered faster, fishing faster, boats better, buildings cheaper, armies cost more/Cannot choose Ecclesiasm government style, Artistic cultural style, or Spanish foreign ally/Unique units: Ulan (Reformation/Imperial), Cutter (Gunpowder/Humanist), Ketch (Reformation/Imperial), Auxiliary Zouave (Imperial), Lombard (Humanist/Reformation), Osterreich (Imperial)

Milan: All food gathered father, lower Army Happiness, buildings cheaper, buildings have more HP, armies train faster, armies weaker, technologies cost more/Cannot choose Democracy government style, Militaristic cultural style, or Holy Roman foreign ally/Unique units: Provisionati (Gunpowder/Humanist), Hargelatier (Humanist/Reformation), Brummer Cannon (Reformation/Imperial), Auxiliary Cannon (Imperial), Auxiliary Musketeer (Imperial)

Humanist Age: Choose your Government Style

Monarchy: Lower Villager Happiness, Higher Army Happiness, gold mined faster, army stronger, army costs more, buildings cost more

Aristocracy: Higher Army Happiness, slow trickle of gold, army costs less, army weaker, buildings weaker

Democracy: Higher Villager Happiness, Lower Army Happiness, army costs more, villagers gather all resources faster

Ecclesiasm: Higher Villager Happiness, Higher Army Happiness, army weaker, buildings have more HP, gold mined slower/Unique Buildings: Cathedral/Unique Units: Bishop (Reformation/Imperial)

Reformation Age: Choose your Cultural Style

Economic: Higher Villager Happiness, all resources gathered faster, resource buildings cost less, buildings built faster, armies weaker

Militaristic: Lower Villager Happiness, Higher Army Happiness, all resources gathered slower, villagers slower, armies stronger, armies cheaper/Unique Units: Corporal (Reformation/Imperial)

Artistic: Higher Villager Happiness, Lower Army Happiness, armies cost more, technologies cheaper, technologies researched faster, villagers faster

Imperial Age: Choose your Foreign Ally

France: Auxiliaries-Voltigeur, Launtier/Lower Villager Happiness, buildings cost more, technologies cheaper, villagers cheaper

England: Auxiliaries-Highlander, Pistoleer/Lower Army Happiness, army trains slower, army stronger, buildings stronger, siege weapons cheaper

Spain: Auxiliaries-Tercio, Conquistador/Lower Villager Happiness, Higher Army Happiness, army trains slower, gold mined faster, trade generates more gold

Holy Roman Empire: Auxiliaries-Mannlicher, Hagabusher/Higher Army Happiness, gold mined slower, wood gathered faster, farms faster

Units:
Gunpowder Age:
Barracks:
Hand Cannoneer-Ranged infantry
Arquebusier-Ranged infantry
Arbelester-Ranged infantry (Counters ranged infantry)
Spearman-Melee infantry (Counters cavalry)
Footman-Melee infantry
Scutari-Melee infantry (Naples patron only)
Provisionati-Ranged infantry (Milan patron only)

Stable:
Chasseur-Ranged cavalry
Corselet-Ranged cavalry (Counters melee infantry)
Cavalier-Melee cavalry
Light Cavalry-Melee cavalry (Counters ranged infantry)
Holy Knight-Melee cavalry (Rome patron only)

Seige:
Catapult-Ranged siege
Petard-Melee siege
Ballista-Ranged siege (Naples patron only)

Auxiliary Center: (Florence patron only)
Auxiliary Chevalier (Florence patron only)-Melee cavalry

Church:
Pastor-Priest

Town Center:
Militia Arquebusier-Ranged infantry (Florence patron only)
Militia Pikeman-Melee infantry (Florence patron only)

Dock:
Fishing Boat-Fishing boat
Trade Boat-Trade boat
Transport-Transport boat
Galley-Ranged Warship
Boarding Ship-Special Warship
Cutter-Ranged Warship (Genoa patron only)

Humanist Age:
Barracks:
Hand Cannoneer-Ranged infantry
Arquebusier-Ranged infantry
Arbelester-Ranged infantry (Counters ranged infantry)
Spearman-Melee infantry (Counters cavalry)
Footman-Melee infantry
Pikeman-Melee infantry (Counters cavalry)
Fusilier-Ranged infantry
Swiss Guard-Melee infantry (Rome patron only)
Papal Guard-Ranged infantry (Rome patron only)
Scutari-Melee infantry (Naples patron only)
Sicilian Gunner-Ranged infantry (Counters melee infantry) (Naples patron only)
Lombard-Melee infantry (Counters melee infantry) (Genoa patron only)
Provisionati-Ranged infantry (Milan patron only)

Stable:
Chasseur-Ranged cavalry
Corselet-Ranged cavalry (counters melee infantry)
Cavalier-Melee cavalry
Light Cavalry-Melee cavalry (Counters ranged infantry)
Hussar-Melee cavalry (Counters ranged infantry)
Cuirasser-Ranged cavalry
Holy Knight-Melee cavalry (Rome patron only)
Reiter-Ranged cavalry (Naples patron only)
Hargelatier-Ranged cavalry (Milan patron only)

Seige:
Bombard-Ranged siege
Catapult-Ranged siege
Petard-Melee siege
Ballista-Ranged siege (Naples patron only)

Auxiliary Center: (Florence patron only)
Auxiliary Chevalier (Florence patron only)-Melee cavalry

Church:
Pastor-Priest

Town Center:
Militia Arquebusier-Ranged infantry (Florence patron only)
Militia Pikeman-Melee infantry (Florence patron only)

Dock:
Fishing Boat-Fishing boat
Trade Boat-Trade boat
Transport-Transport ship
Snow-Ranged warship
Boarding Ship-Special warship
Galley-Ranged warship
Cutter-Ranged warship (Genoa patron only)

Reformation Age:
Barracks:
Pikeman-Melee infantry (Counters cavalry)
Fusilier-Ranged infantry
Musketeer-Ranged infantry
Halberdier-Melee infantry (Counters cavalry)
Rocket Arbelester-Ranged infantry (Counters ranged infantry)
Corporal (Militaristic cultural style only)-Melee infantry
Morisini Halberdier-Melee infantry (Counters cavalry) (Venice patron only)
Morisini Musketeer-Ranged infantry (Venice patron only)
Condottieri-Melee infantry (Florence patron only)
Swiss Guard-Melee infantry (Rome patron only)
Papal Guard-Ranged infantry (Rome patron only)
Sicilian Gunner-Ranged infantry (Counters melee infantry) (Naples patron only)
Lombard-Melee infantry (Counters melee infantry) (Genoa patron only)

Stable:
Hussar-Melee cavalry (Counters ranged infantry)
Cuirasser-Ranged cavalry
Rider-Melee cavalry
Dragoon-Ranged cavalry
Cavalry Corps-Ranged cavalry (Counters melee infantry)
Saber Cavalry-Melee cavalry (Counters ranged infantry)
Reiter-Ranged cavalry (Naples patron only)
Ulan-Melee cavalry (Genoa patron only)
Hargelatier-Ranged cavalry (Milan patron only)

Seige:
Bombard-Ranged siege
Cannon-Ranged siege
Bombardiere-Ranged siege (Venice patron only)
Brummer Cannon-Ranged siege (Milan patron only)

Auxiliary Center: (Florence patron only)
Auxiliary Cavalry (Florence patron only)-Melee cavalry

Town Center:
Militia Musketeer-Ranged infantry (Florence patron only)
Militia Halberider-Melee infantry (Florence patron only)

Church:
Priest-Priest

Cathedral: (Rome patron or Ecclesiasm government style)
Bishop (Ecclesiasm government style only)-Priest
Cardinal (Rome patron only)-Priest

Dock:
Fishing Ship-Fishing boat
Merchant Ship-Trade boat
Transport-Transport ship
Galley-Ranged warship
Galleon-Ranged warship
Plated Boarding Ship-Special warship
Frigate-Ranged warship
Privateer-Ranged warship (Naples patron only)
Ketch-Ranged warship (Genoa patron only)

Imperial Age:
Barracks:
Musketeer-Ranged infantry
Halberdier-Melee infantry (Counters cavalry)
Rocket Arbelester-Ranged infantry (Counters ranged infantry)
Grenadier-Ranged infantry
Fucile-Ranged infantry (Counters melee infantry)
Corporal (Militaristic cultural style only)-Melee infantry
Morisini Halberider-Melee infantry (Counters cavalry) (Venice patron only)
Morisini Musketeer-Ranged infantry (Venice patron only)
Condottieri-Melee infantry

Stable:
Rider-Melee cavalry
Dragoon-Ranged cavalry
Cavalry Corps-Ranged cavalry (Counters melee infantry)
Saber Cavalry-Melee cavalry (Counters ranged infantry)
Carabineer-Ranged cavalry
Shock Cavalry-Melee cavalry
Ulan-Melee cavalry (Genoa patron only)

Siege:
Cannon-Ranged siege
Howitzer-Ranged siege
Mortar-Ranged siege
Bombardiere-Ranged siege (Venice only)
Osterreich-Melee siege (Genoa only)
Brummer Cannon-Ranged siege (Milan only)

Auxiliary Center:
Auxiliary Roundshier (Venice patron only)-Melee infantry
Auxiliary Cavalry (Florence patron only)-Melee cavalry
Auxiliary Jager (Rome patron only)-Ranged infantry
Auxiliary Lancer (Naples patron only)-Melee cavalry
Auxiliary Zouave (Genoa patron only)-Ranged infantry
Auxiliary Musketeer (Milan patron only)-Ranged infantry
Auxiliary Cannon (Milan patron only)-Ranged siege
Auxiliary Voltigeur (France foreign ally only)-Ranged infantry
Auxiliary Launtier (France foreign ally only)-Melee cavalry
Auxiliary Highlander (England foreign ally only)-Ranged infantry
Auxiliary Pistoleer (England foreign ally only)-Ranged cavalry
Auxiliary Tercio (Spain foreign ally only)-Ranged infantry
Auxiliary Conquistador (Spain foreign ally only)-Melee cavalry
Auxiliary Mannlicher (Holy Roman Empire foreign ally only)-Ranged infantry
Auxiliary Hagabusher (Holy Roman Empire foreign ally only)-Ranged cavalry

Church:
Priest-Priest

Town Center:
Militia Musketeer-Ranged infantry (Florence patron only)
Militia Halberdier-Melee infantry (Florence patron only)

Cathedral: (Rome patron or Ecclesiasm government style)
Bishop (Ecclesiasm government style only)-Priest
Cardinal (Rome patron only)-Priest

Dock:
Fishing Ship-Fishing boat
Merchant Ship-Fishing boat
Transport-Transport ship
Galleon-Ranged warship
Frigate-Ranged warship
Plated Boarding Ship-Special warship
Battleship-Ranged warship
Ironclad-Ranged warship
Galleass-Ranged warship (Venice patron only)
Privateer-Ranged warship (Privateer patron only)
Ketch-Ranged warship (Genoa patron only)

So feel free to ask me questions, give suggestions, or anything like that.

I warned you it was a long read