This is my first game so everything you said is really valuable. My artistic abilities aren't too great so I tried to keep the graphics/colors as simple as possible which actually constrained some of the gameplay a bit since, as you said, some of the mechanics like different enemies/powerups can be difficult to interpret. Thanks for playing and for the feedback, I really appreciate the time you took to do so!
And I am thinking about adapting it to mobile once I tinker out a good enough control/aiming scheme. I think it would work well.