Hi,
in general I like the game style and mechanics. Right now its a good start and I would see a lot of potential in the diffrent areas to expand functions.
It was a bit confusion to how much HP you need to destroy to get one XP (proportionally). It's increase (more HP per XP) if you destroy bigger rocks. That is a bit counterintuitive to me (harder rocks should give more XP and not less due to the higher difficulty) AND it is less rewarding as you spend overproportionally more time with bigger rocks to have the same result (it takes longer time and then you get less XP in the end).