Enjoyed this quite a bit, had to pull myself away from going any further!
Did get a bit repetitive, but as others have said more guns, more abilities, more time to develop, would help that!
One critique I have is that the next wave starts and they begin attacking you while the round popup is still blocking your view/reticle. You could address this by having the round start UI be at the top or top-middle instead of the middle. That way, even if the timing overlaps when combat begins, it doesn't block the player from fighting back! Though this wasn't a huge issue.
I really liked how accurate the hit scan is and how the graphics/pixelation are the distance/accuracy limiter instead of the gun's range! Very neat touch!