I dunno why anyone said nice...
Super duper amazingly boring. This game is pretty crappy. You can find 100 other games exactly like this that are a whole lot better. This has no change, no feelings. It's click, shoot, no upgrades, no really hard enemies, it's lame.
Constructive criticism:
Put an upgrade system into the game, either something like power ups after killing enemies, or a buy between rounds system. Also change the feel of the levels, new tilesets ftw.