Fun game. Would love to try multiplayer sometime.
Three suggestions, add a respawn option on death, so instead of going back to the splash screen I can jump right back into the action without waiting.
Maybe add a "safe zone" around the player that prevents enemies from spawning. Almost every death I took was caused by someone spawning right next to me and cheap shotting me.
Lastly I didn't see an obvious way to heal damage. Maybe in the upgrade menu add "heal for XX scrap"?