That one had some annoying puzzles towards the end, I can see a lot of people having trouble with one in particular.
It really bumped up the combat challenge too. I'd only had one game over before this point, but the shadows with the corrosion skills got me a few times, especially when paired with the ones that block damage.
The boss seemed fairly tame compared to a couple of the earlier optional ones, but still a fun fight, or I might have been slightly overleveled after a lot of running around trying to solve the final few puzzles, I still need to go back for a quest that I need to complete to 100% map the final floor.
Dialogue wise the "haha, you're pretending not to be scared but you actually are" got old after a short while.
Overall, a pretty decent dungeon though, especially visually; It wouldn't have felt out of place in a pure horror game like Corpse Party. I liked how the FOE mechanics were tied into the dungeon's theme too, this game seems to be doing a lot more unique things with them than the Etrian games that I've played.
I think Atlus went slightly too far with the puzzles at the end though, unless there was a giveaway clue that I overlooked.