Just put a solid 20 minutes into it. Here are some quick impressions:
It's a really simple concept that anyone can enjoy, which is perfect for the iPhone. I like how if you really think the physics through, you can solve each puzzle on your first try. That being said, there's a fair amount of randomness as well. It's a solid concept and addictive enough to keep anyone's attention for a few minutes here and there, which, again, is primarily what most iPhone games are meant to do. Though, I'd like to see a little more depth in the gameplay. Granted, I haven't made it past the medium stages, but assuming the rest of the game plays the same way with only changes in level design, I think it'd be nice to vary the gameplay up a bit. I can't really suggest how, beyond some simple collectable powerups, like maybe a "stone" powerup that temporarily locks a falling piece in place on the screen, potentially blocking the purple star from falling into the water. Or maybe a "rapid tap" powerup that temporarily allows the player to click away multiple pieces in a short amount of time, disregarding the timer. Of course, these would end up changing the game quite a bit, so forgive me for suggesting something that might have already been considered.
The visuals are fantastic. I love the pseudo-Japanese look, and the whole product has tons of polish. It's a nice happy theme, and I think it works great for this type of game.
I'm not quite as fond of the marimba-like audio, however. It gets old after a while and there's no real tune to latch on to.
Overall, it's really a fun game and perfect for the iPhone. I can't see myself playing it very much after I beat all the levels, but it's totally worth the 2 dollar pricetag.
Well done on your first iPhone game! Hope to see a lot more from you in the future! =)