, don't you miss moments like these? (0:15 -> http://www.youtube.com/watch?v=B0YpAkbI_W4)

Games likes Twisted Metal are nice I think. Should not be too much work if do a few unique cars (like 6 to choose from).

Maybe something like virtual cop or house of the dead gamestyle with some original weapons. A bit more work I quess, with all the mapping and scripting. Although an random gameplay mode could be added (randomized enemies, items, the different routes to take) to give it some replaybility and that it doesn't get old to fast for the gamemaker (than you have atleast one happy customer :P).

Or maybe some horror/puzzle game like The 7th Guest.

, this sounds cool, reminds me a bit of this http://phoenix.ee/gallery/photos/Unreal%20Tournament/955436898-1.jpg. That was a map with 3 skycrapers where you could jump from one to another with low gravity. Very fun to play.