I was pretty impressed by this game. My main complaint was that it probably could have used better graphics. I do have to appreciate how you have so many different good songs. Everything is clear cut, easy to understand. You could use sound effects, though. You would be surprised at how much you can get addicted to it.
I liked the way the enemies exploded. You had a nice amount of time to prepare for each wave. I like how the guns just randomly go around when there's no enemies. It's nice when the game just plays itself. All in all, quite enjoyable.