I had a go at your game. :)
Here are my thoughts-
* The sensitivity needs to start in the middle of the bar, not at the lowest. I played a fair bit struggling with super low sensitivity before I even saw I could change it at the start menu. It might be obvious to you, but a first time player isn't looking for a sensitivity option in the first menu, they are looking for start game or how to play.
* There is a bug that makes it so when I pull my mouse over to the side, it goes onto my 2nd monitor and I'm no longer controlling the game anymore. This was the cause of most my deaths.
* More feedback on being hit my enemies would be helpful, as it was, it just felt like I died for no reason. I had no idea where the enemy was, I didn't know if I stood on one, or it shot me. My hp bar just seemed as tho it was randomly jumping down.
* Obvious things like sound effects and so on, but I'm guessing your working on that already.
If you need some clarity on what I've been saying, don't be afraid to ask!
Good luck! :)