Despite being one of the most avid posters in this thread, I still give the game a solid: Don't buy. (not even a try before you buy), because the game IS solid, but very limited. There's only so far the puzzle mode can keep you interested, even with the possibility of of infinite puzzles, and the challenge mode seems more like trial and error rather than good gameplay, with a bit of annoying controls thrown in. Not that the controls suck, but you may need to to a bit of calibraiton outside the game to get it to work best - it's not so much that touch is bad, but for a game where you need to playthis fast (on later levels), you want to be as accurate as possible.
However, it looks as I'm alone on this. I DO play it a lot, and it's not bad, it's just I don't think I got my money's worth, and keep wanting to play it more just to justify the price.