A 4/5 from me. The game is addicting via simplicity. The goal, gameplay and design is so simple, that it's fun. I could play this for hours without getting bored.
The reason why it's not a 5/5 is because it lacks variety. Would be cool to have things like random asteroids, or asteroid belts and such. It's just stars, planets bigger stars, bigger planets and so on.
All in all, great game. I hope to see more from you.