Very nice work. I thought it was a pretty good concept with nice appeal. I think it would make a good sit down VR game. As for recommendations on improvements, here's a list of things I would consider picking a thing or two out of:
1) Keyboard controls -- due to the nature of the game, you're repeatedly needing to lift your mouse up and bring it back to the other side of your work area so you can continue spinning in a certain direction. Arrow key controls (or any two keys really) would alleviate that and allow you to use the mouse in a more traditional FPS-style.
Also, perhaps spacebar as an alternative button to "fire"?
2) Perhaps a few "weapon" models with various rates of fire? You could possibly use varying reload speed to add new complexities -- I'm not 100% sold on this idea, but it warrants thought.
3) Powerups of a sort would be worth considering.
4) Maybe extra "push" for scoring headshots? Admittedly, I spammed and just shot from the hip like a damned wild-man, so maybe this is already in there and I didn't notice it :-P
5) Lastly, consider a small tutorial and/or an "How to play" explanation on the main menu. The main benefit of this was that it took me a second to realize there was more than one spawner and I had targets ramming me in the posterior. :-)