simple but fun. I liked the art

Cool game, it  would be a lot easier if you shoot with left mouse button. :-)

Looks very cool so far!

One thing I'd like to suggest is to perhaps rework the character controls slightly, as it feels quite unnatural in my opinion. Maybe have the character move in different directions with WASD/arrow keys, and shoot where the mouse points (think 'Nuclear Throne' or 'Enter the Gungeon'), that would make it a lot easier to kill the bad guys, and also make the controls feel better.

Good luck :)