Few Things you could fix...
Man i could just be me but i couldent get past the first level without dieing... it was so long, i got up to like 46 kills on the one level and the whole building was falling apart... you hsould make it shorter cuz people will get frustrated that they cant beat the first level.
The music got quite repetative after a while, make a longer song, or have several songs to compensate.
It was quite well done however but those things should get fixed to make the game more of a hit.