Brilliant!
This is one of the best games I've played on Newgrounds for a while! I know the same type of game has been done before, but this puts a new edge on it, and it is really fun to play! The only criticism I can think of is perhaps to add some music, but the sounds are good enough on their own really! Maybe a password option to get back to the later levels easier?
Anyhow, this is fantastic!