It's kind of a rhythm game, so playing without sound is definitely going to lose something. I used to love Geometry Wars 2 on xbox, and this reminds me of some of the more puzzley modes that game had.

A more traditional game that's really good is that new Rayman runner/platformer that they show as a featured game in the app store. Awesome graphics and it's really fun and addictive. Playing it, you can imagine how a Super Meat Boy might work perfectly on an iPad. (It's not as crazy as SMB!)