Really nice way to spend your time instead of working!
My main complaint would be that you can't turn the music off without turning off the sound effects. That really annoyed me.
Besides that, I sometimes had the feeling it's a little unbalanced. Some waves I had to redo 3 or 4 times, while some other waves after that I got through without barely a scratch.
And like some others mentioned, it would have been cooler if all the weapons remained bullet based. If only to stick closer to the source material.