Auditorium is that rare kind of game that's a must-play no matter what kind of gamer you are. It's a puzzle game, a music game, and a piece of art at various times. It's out now on the iPhone courtesy of EA (and the main download is absolutely free), but even if you don't want to take up space on your mobile device, just head over to the website and play the Flash demo for a little bit. My guess is that you'll be taken by the beauty and originality, at least enough to pop over to the App Store and download the main game.
The idea is that there is a stream of music flowing through each level, and it's your job to use the various widgets you've been given to shape and paint the music into certain spots on the board. As you move through the levels, you'll get more and more adept at sending the flow where you need it to go. Fortunately, the puzzles get harder and harder as you play, creating a great curve of both learning and adjusting your mind enough to find the right solution.
The main game is free, and then you can purchase all of the levels in three different packs, at 99 cents each. But even for the whole three bucks, this is quite an experience; it's more than worth the price. Again, if you're doubtful, give the demo a try, and see if you're not convinced to try the whole thing in order to see where it goes.