This is a pretty solid little shooter and a nice use of the sprites in 3D. The vivid color scheme is great.
I don't play a lot of FPSs so my expectations may be off but the mouse seemed much too sensitive. It was almost impossible for me to keep the gun pointed at anything, especially if I was moving at all.
It would also be nice to have some health indication. By the time I reached the central building I'd basically decided I was invincible because hits didn't seem to do anything, but the bullets from the boss did finally kill me.
One of the few things that bothered me about the look and feel was the dark texture that was used in a few places, I noticed it on the ramps leading up to the main platform. It had a very fine texture that ended up looking noisy to me. Didn't feel like it matched the coarser more open textures elsewhere.