I'm really enjoying Trine so far... I'm only a hand ful of levels through, but I've enjoyed it quite a bit along the way.
The game is basically a platformer, but it gives you 3 characters that you can play with to get through the levels. Each level seems to introduce a new mechanic, and those mechanics help you solve the puzzles in the environment that will help you progress. Somewhat similar to Braid in that respect.
So far the game has been a great casual game for me to play when I don't have a lot of time to game. The quality is VERY high for a game in the $20 range, it has a cute fantasy story with funny voice acting, and it's a good quick in and out kind of game.