Y'know...it's not awful.

I like it. The biggest complaint I have is how low-quality the background is. The image is was too big and low-res and you can clearly see where you repeat the image. Two suggestions I have are:
1. draw your own background, it'd probably look a lot better.
2. maybe zoom out just a little. The screen feels a little cramped. Oh and have a more dynamic camera. It adds greater effect to shift (not shake) the camera a little when someone is hit and maybe follow them a little.