Swinging the axe is REALLY FUN.

The upgrade tree is difficult to navigate. I would appreciate it if icons for upgrades I can't purchase are greyed out so I can more easily see what I can purchase.

The loop was basically: Clear map -> Upgrade -> Repeat.

A little tedious after a while moving my mouse hand around so much, maybe some upgradable automation could alleviate that (if it's not in already, again had a hard time with the skill tree).

Try making it so tooltips stay within the game window. Often times I had to reposition the skill tree to even read what a skill did.