I added mountains, 1 to 3 depending on the difficulty setting and the landing pad gets smaller with difficulty as well. I'd like to get back to this at some point and do the scalable mountains with landing spots that give points based on the difficulty of landing on them (and at least add some sound to it). The little things I learned about ship movement helped me with the Asteroids clone I'm working on.
https://www.youtube.com/watch?v=qKSV9queYYA