Nice game, but here are a couple recommendations just off the top of my head:
• Decrease the time it takes to reload. It's kinda annoying having to wait for a reload in an arcade gun shooter.
• Give the player some i-frames after being shot, so that they have a little bit of time to recover from a mistake without losing health immediately.
• The enemies' kneeling animation needs to be smoothed out a bit. When they go down on one knee, it's as if their head is teleporting to another location, which can cause the player to completely whiff on a headshot.