Thanks for the feedback, it definitely helps! Do you have any tips how I could improve these issues?
Hm, maybe try to have the ship not rotate around its own axis due to gravity, but due to player input only.
And then maybe I'd speed up the incoming planets, play around with their HP stats until it feels fast-paced and build in times where more planets come and where less come (so the player can breathe in-between).
Those are ideas of mine, see what appears useful to you as the game designer and what you like and what not. After all, I'm just one player giving feedback :-)