Quite good!
I liked this game and I finished it on my first go.
To improve it, you really have to put in good sound, look in the audio portal for some. You could add a better background and make different shapes which would make the game difficult. You could add highscores so you could time how long someone takes to finish levels and then submit it, to see who is the fastest.
See if you can put any of these improvements in the next version (if there is going to be a next version).