Some quick feedback;
- Performance dipped heavily after getting several upgrades
- Players projectiles obscure the screen, I suggest making them visually smaller or semi-transparent
- Really needs mouse sensitivity setting
- UI warning that enemies are behind player would be helpful, maybe a short range minimap showing enemies. Also a directional damage indicator would also be nice
- Enemies can spawn too close to the player
- Sometimes enemies seem to just move extremely fast in a random direction
- Some weapons/projectile types did not seem to be doing any damage, made some runs unwinnable
If you happen to need any inspiration, consider taking a look at Still Not Dead: Prequel, which is a similar style of game