Very nice game. I can see this become a very nice casual mobile game.
I absolutely loved your level design and the gradual increase in difficulty. The chiptune music was very nice, it would make the game even greater to have some more soundtracks if you plan to release the game on mobile. You could also add different word themes and after some levels a simple enemy type.
(P.S. I would appreciate it if you could try out my game)
Keep up the good work (9-^)