It's an alright game. However, I have several issues:
1)There is no progression. It doesn't feel like the enemies spawn more often the longer you play and new types of enemies don't appear, either. I would probably add new enemy types gradually, based on the player's kill count: you got 100 kills - big squares start spawning, you got 200 kills - shooting squares start spawning and so on.
2)Grenade launcher can damage you as well, but it's not explained in the slightest. It got me several deaths to realize it.
3)When explosive enemies spawn at your position or right in front of you, it's the biggest bullshit, cause you die and can't do anything about it. I would spawn them outside the playing area or give them "spawn protection time", when they can't hurt you and you can't hurt them, either.
I also think that background music and a leaderboard would be nice.