I liked the Idea
but I think it still needs some work. Here are some things you could work on:
Sound: add some. Games without sound just aren't as appealing as those with it. You could either do awesome background music or actually take the time to create sound effects for things. Either way, it would be a major improvement.
Gameplay: I don't know if this was a style choice or what, but guns fire more than one bullet at a time. Yours should too. Unless you purposely chose to make it fire only one bullet at a time, I would suggest fixing this. You could possible make the gun have a clip, so that you would be slowed by a reload after so many shots, but the whole one shot thing is fairly annoying.
Possible Glitch: I can hit next wave before the wave actually ends. And it clears the current wave. You may want to look into this, as I don't think it's good that someone can just automatically skip to the last level...