The backtracking, the lack of clear guide of where to go, and the punishing combat. Combine them all and every time I try to play this game, I get stuck somewhere.
On this most recent attempt, I reached the Mantis Lords but found the fight 1000x times harder than what came before, barely being able to get past the first phase. Also getting TO the boss requires dropping down past flying annoying enemies so it's not like you can re-try it.
So I figured I'd come back after powering up. I went elsewhere and defeated the Soul Master. Then I had enough souls to buy the lantern, so on my way backtracking all the way to the start to buy it, I made a wrong turn and dropped down somewhere in a new area. Now I can't get back up. And that new area is actually pitch black dark, and of course I was just about to buy the lantern. So... now what... I would have to fumble and keep dying in the dark to try to find a way back and then re-grind for all those souls? F*** that.