It's as simple as it can be, but it's nice that you made a level for every single planet (even though the levels don't differ that much between each other).
I can't quite tell what the main character is supposed to represent (yellow scribbles?), and the background is a bit blurry. Collision detection can be a bit off at times, especially in the Mercury level (you crash even though you don't even touch the barrier).

Mainly though, the movement could be made more fluent (+ possible acceleration, inertia) instead of moving by a fixed distance in four directions.
Graphics look a bit amateurish (MS Paint) and the medal doesn't seem to work.
I don't know what's going on when you complete all levels…

It's an okay game, but it could definitely be improved in many ways.