Such an engaging game! Had just 1 hour to play and ended up spending it all trying to finish it hehe (the A+Z trick was a nice touch, by the way).
Loved the tutorials and the art!
On the other hand, that final level, wow, it was tough. Had to retry many many times. It felt really good to finish it, though, like the one you get when you finish a Guitar Hero 2 song in hard mode and with 4 stars.
What might make the experience even better is for the pieces to always rotate 90 degrees every few frames, and for the player to be able to speed it up with space (the game would have to make sure there's no need to rescramble the pieces). It might give it a Tetris feel, so who wouldn't want that? :)
Oh! And, since most of the mechanics are centered around the keyboard, and it's very likely one'll have to restart the current level pretty frequently, the player should be able to select the levels with the arrow keys and press Enter to start playing. Having to use the mouse just to start again felt a bit annoying sometimes.
It was really fun, and with the right amount of challenge thrown in to the mix ,:)