Another great game by Valve. Not much to say besides you should own it and play with me sometime.

Awesome game. The wonderful art style compliments the nature of the game and is completely unique. You should buy this game and play it all the way through at least once. If nothing else, download the free demo and see what it is all about. The game progresses quite a bit past the demo but it gives you a good idea of the overall feel of the game. Do it.

A very laid-back game that can be as intensive or relaxing as you want. You pick the music and the level is generated from that. Nice because you can play a level or two without needed to get invested. Not saying you won't get addicted, though...