I finished it!
Great game. A timewaster like I haven't seen in ages. Kudos to you, sir. =)
The lesser points:
-the beginning is quite hard and annoying, and it takes a while before you can upgrade yourself enough to pass through with ease- but once you do, you go through whistling.
-Once you've got a new head upgrade, it either kills them one-shot, or the routine two-shot doesn't change at all but for a larger portion of their health bar missing. Maybe this could've knocked them back a bit more?
-The sword->axe upgrades don't make any difference at all, apart from vs. the final boss, who was annoying, by the way.
But most of these points were minor enough for me to still have a good time.