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