It's a bit hard to play, but perhaps it's just because the first level is already with some enemies. A suggestion would be to create 1 or 2 levels which would be very straightforward to solve, for people to get used to the controllers.
Besides of that, I liked the level design potential, it could look very nice with more thematic art =)
Nice that you're gonna update it.
So, by thematic art, I mean choosing some specific themes to build upon. Perhaps having a futuristic theme? Then the scenario could be made of iron, the player objects could be robots, the enemies could be enemy robots, etc
Or perhaps the game happens on a mountain? Then the scenario would be pure ground and rocks, the characters could be animals which live on the mountains (one inside a ball and the other on top of the rocket?)
Things like that
