This idea worked really well as a map for warcraft 3. Basically, you use the game engine and AI to make a series of minigames, wherein points are scored and the player with the most points wins. As reward for winning, the player gets to CHOOSE a few minigames, whereas the rest are random. The minigames are usually completely unrelated to the game, but utilize more or less the same control scheme. For example...
A game where the players are all humans, trapped in a pit. Above them, are advanced goons which fire very slow projectiles. At first theres only one goon, and then two, and then three, until pretty soon the humans are trying to dodge tons of bullets. The last one standing wins. Then the next one starts up.
What do you think? Not too horrible? You won't flame me to the point where i'm just socks full of ashes?