Nice game! The concept is nice. I agree with the comments about the restarting. The countdown is a nice touch, but maybe add an option to be able to press a key to immediately restart.
I kinda missed some overview about what galaxy was where and how to find them when I (finally) found a moon. And I missed some visuals to indicate I was at the bottom level ... fell of too often and got frustrated :D
But great first submission. Congrats on finishing a game!