I had fun...
Although there are key flaws in the game, it was still relatively enjoyable.
There was no plot, something that often annoys me. The gameplay is utterly derivative. If you're going to utilize a concept that has been done plenty of times before, it's usually preferable to put some sort of spin on it, to make it interesting. The backgrounds were utterly bland and uninteresting.
There doesn't seem to be any variety in enemies (Although I might just have not gotten far enough into the game), which makes the whole thing feel rather genetic. The lack of music is also frustrating. Even a rather generic or irritating tune is preferable to none at all. Finally, don't put the percentage of killed enemies. I really don't care how many enemies are left enough to decipher the percentage points; I just want to kill the ones that are in front of me.
The game is mildly fun, and with some effort, could be decent, at least. With what's there however, it simply isn't.