Great game, but short. The upgrades are good, but I would add one more that improves your movement (like jumping or teleporting), and maybe a stunning ranged weapon.
Very nice. The game is clean, fun and easy to play, but you should consider adding choices of skill perks as you level up. But the general ideia for the game shows great future. I'll wait for a new version.
 "Zombie at the Gates"){kind=icon}
 "Nightmare Runner"){kind=icon}