Nice job! The shooting felt good, it was just dark enough and I like the way the monsters look. The biggest downside for me was that the monsters don't make any noise (that I heard) as they get closer to you so I would find myself surrounded pretty easily and dying pretty fast. Like Kenneth mentioned, some positional sound would be awesome. An ammo counter would also be nice. I also didn't think the music fit too well. Maybe something more frantic or aggressive?
I liked 'purchasing' the door to expand the map and another idea for expanding the mechanics could be the ability to destroy the hives, but more could be spawned as the waves increase?
Good work!