SUPER MARIO
Everyone should at least try this game, (the link is in the title). I'm sure most people know a bit about Super Mario and have played it before, however for those that haven't, I'll explain a bit about it, including the very enjoyable Level Editor.
In Version 3.0 Level Editor, there is a multi-level scenario in which Mario (or Luigi) must fight, run, leap and bounce his way through. This is a good place to start if you aren't great at the game.
The Level Editor is where the game goes beyond an ordinary single-player platform game and into one that is shareable and able to let players compare their skills. The Level Editor is, as the name suggests, a level editor. In it you can choose your own backgrounds, make your own platforms, choose which animals and monsters await Mario, choose Mario's start and finish points, build bonus levels and make Warp Points. You can even choose where and how many coins will be in the level.
I've included my own level; JUMP OR DIE, to show how easy making levels are. If you can finish the level, your skills are quite good. I would appreciate others making and sharing their own levels, however, if you are going to distribute the levels in files (as I have done), please make them .doc files with only the codes and creator's name in them.
Levels
///~~[Crusading Knight]~~\\\
\\\~~[Crusading Knight]~~///
And when he gets to Heaven,
To Saint Peter he will tell,
One more soldier reporting Sir,
I've served my time in Hell.