To add to RedWorldGames's feedback: The game is fun, but there's something you should take into account in case you make a game like this again: Make sure to give the player feedback when they are hit, like a red flash on the screen and/or a hurt sound. Its just hard to tell you're being hurt when the slimes are behind you. Also it wouldn't hurt to make it clear that upgrades give some ability to you, for example: the upgrade that "increases health gained from killing enemies" made me think that you get health from killing enemies always and this upgrade would just improve that, instead of granting it in the first place.