The fifth chapter is where, before Patch 1.1, the game started to get notably buggy. With impassible doorways, unresponsive NPCs, and quests that wouldn’t trigger. Difficulty-wise though it’s remarkably easy overall and a high armor class actually ends up useful. The fifth Ancient Curse segment however gives you a preview of just how much more unfair the encounters can get by introducing enemies with paralyzing auras and touch-based ray attacks which deal sneak attack damage and cause blindness.
The sixth chapter is filled with those enemies, and pre-patch it was a nightmare to navigate. Post-patch it’s much more doable as the paralysis can be avoided with the Blight Fight feat, the blindness is no longer permanent, and the teamwork feats that turned them into living machine guns were changed. The chapter’s still a massive slog though; an incredibly unfun hack & slash deathmarch with annoying puzzle aspects tacked on (I never was able to figure out how to get behind that locked door at the southern end of the 2nd floor, across from the basement steps). Though to be fair a large chunk of the enemies can be avoided if you know exactly where you’re going.
Depending on your choices, the game can conclude right after defeating the boss of that last chapter. Which is the way I went with this first playthrough (fiend-blood Eldrich Scion) since the team was suboptimal in a large number of ways and I didn’t want to slog through even more annoying enemies in the seventh chapter. My second playthrough (which was started while waiting for the 1.1 patch to fix the chapter 6 progression-blocking bugs) with a Scaled Fist/Knifemaster/Sword Saint is currently in Armag’s Tomb, and that’s the one I plan to take through the seventh chapter.