Great idea! I really liked the backdrop of space. It was really peaceful when floating between planets. Collecting rings on the planets was a fun secondary objective, and each planet felt a little different based on the speed and sense of "gravity". The surface textures were pretty cool. Maybe you can add even more personality to the other planets, like different music or ambient sounds, so they each feel like a new stage.
^ Me, when I flew past Earth and next into the Sun ...
I had fun playing! The only other note is: no love for Mars or Venus? :o