Agree with the above comments. Looks slick, simple to play etc...
Perhaps the first 25 levels are too similar though, as in too easy. My son, who is 14, glanced over to see what I was playing and said it looked boring (although he's probably not your target audience).
The game gets much better from level 26 onwards but I'm the type of person who downloads quite a lot of games, I'll play for 10 mins or so and if it doesn't hook me I just delete it and download something else.
10 or so of the simple levels would probably be enough before you introduced more blocks or another aspect to the puzzles.
Loved the fact that there were no ads until level 30.
The animations and sounds are pretty spot on and overall it looks really well polished. I'd imagine that this isn't your first app, what other ones have you made?