I really enjoyed the concept, but I think that the progression could be made a little faster (I spent slightly under an hour playing). The skill tree mechanics are well-implemented, but I'd prefer if there was an option to use middle click for moving around the tree. The UI could do with some polishing to make it more intuitive to understand your stats (maybe by adding icons near the text?)
Anyways, I managed to get all upgrades, finished the game without breaking my mouse, and the game was very fun!