This game is awesome! I enjoyed it a lot. It's a pretty original idea I think. I like turning the planet to defend it.
You def should keep working on it and tune it a bit. The main issue is the game will go on forever because the defenses are too good and mining is too easy/fast. The defenses should break down and go away. You should be able to upgrade/sell them.
But this is really good and I ended up rating it one of the best I've played!