I'm not entirely sure why, but I've been replaying Canabalt, a free, browser-based platformer, at least once every two days since it came out.
Perhaps I long to luxuriate in the luscious pixel art. Perhaps I'm desperate to beat my own high scores. Perhaps I'm just in love with the game's pacing (an average playthrough will only last about ten seconds, leaving you ready to try over and over).
The premise is pretty simple: run as far as you can across rooftops and through skyscrapers, using only the X key to jump. Hold it for a high jump, tap it for a short jump. Pretty much what you'd expect, really, save for the fact that you probably won't expect to play over and over and over, even after you've already seen all of the randomized obstacles the game will throw at you.