I think you need to add objectives. So let's say you need to collect X amount of specific sized planets in order to proceed. Then add in some "bad" planets that could damage your planet but not kill you something like the ring system in 2D Sonic games. I think you should also change the controls to WASD/D-Pad. That control scheme feels dated, like the old Resident Evil games on PS1.
Let's face it, the visuals are cute! ;)