The Demon Spawn thing, the final level, was infinitely easier than the previous area in the corrupted forest. Those Mother Trees are the hardest enemy in the game, in my opinion. One of those would kick that demon lord's ass. Personally, I think you should make the final area harder. The King and the Demon Spawn, the areas that are supposed to be the 'final' areas are so much easier than previous areas, especially when you've got 10 command and skeleton giants lol.
Shotgun is waaaaay overpowered. I have this rare level 2 shotgun and I am currently level 10 and I find it better than any other weapon, except for dealing with roaches. 3/5 because it just seems... lacking.
I like the game, quite a lot in fact. Only problem for me is, your own hooks get caught in your propeller. I was on the bridge level, number 8 i think, and I had the last piece of bridge and was dragging it over but my hook got caught in my propeller and killed me. Its an annoying bug.