I thought this game was really cool. I think the balancing/ramp up could use a bit of tinkering. The game seems to start off incredibly difficult. When an enemy spawns, I found it to be nearly impossible to kill it before taking significant damage. I died multiple times on the first moon and had to keep restarting until I accumulated enough upgrades to survive. Then, suddenly my orbit speed got high enough that no enemy could ever touch me and suddenly there was no challenge at all.
I think, in my opinion, that the first moon should be easier (though it's possible I'm just having a skill issue). I also would like some difficulty to continue ramping up as I upgrade so the game doesn't get too easy. Maybe in the later moons there's occasional special enemies that move faster? There's a chance that the game is intended to be idle and if that's the case, ignore that idea!