The previous comments sum up a lot of the things that need work. Most of them are actually easy fixes that immediately improve your game. Having the UI readable at all times and adding sound effects will transform the experience instantly. Currently the player has no idea when they get attacked from behind, because there is no sound cue, and you can't see your health getting lower either. If you focus on fixing those two points first, people will already have a better experience play testing. It's no fun shooting a gun that doesn't go BANG! ;)
Good job on the overall art direction though. Still very rough, but looks promising!