Having a distinct fascination in odd-concept & well crafted games, a friend of mine showed me this great game called Braid.
Its a side-scrolling platform game with one great feature; you can control time. In order to solve puzzles and progress through the various worlds you have to play around with time!
On top of this great concept is an artfully crafted world, and an interesting philosophy.
Check it out:
http://braid-game.com/