Original. Does this need to be stated? This game is brilliant. I saw that you said you wanted to add more to this and I think you should. So far it is simple but there is room for so much more in this game. I would avoid upgrades like most games, as upgrades can actually give the player a disadvantage, I think the random power up/ health packs is great. I would suggest some level depth, such as defeating bosses. I think there is a lot of potential for original boss fighting with this. I wouldn't change anything aesthetically since it is already simple and pleasing to the eye. With level progression I think this game could be really engaging and addicting.
~ The Review Guru