in the middle of book 2 now. Had one "death" and a lot of very close calls. The ap's ability to put the fear of gods in the players is one of my favorite parts, every corner has something new and dangerous to look at and talk to. Before running I'd rec reading the Nhimbaloth article (near the back if you have the compilation. Otherwise the wiki article is fine) and a little on Absalom in case the party goes there. spoilers from here.
Otari's a pretty standard town. Every important npc has art for them. Making sure your players have and read the players guide is a must just so they make sure what mechanical services they have. Ground floor is mostly combat focused, there's two npcs to negotiate with, one's pretty motivationless and the other is very amusing and is planning on invading the town. Cool environment.
There's a potential to go to floor 2 before floor 1, which is very bad if the party looses favor with the cultists. If the gunslinger didn't get like three crits in the big fight they would've tpk'd. Luckily they're non-hostile-ish when you first meet them. Almost every npc here is neutral to the party when they meet, which is great! A lot of very tense roleplay moments! Chandriu will tpk them if they don't run away!
The party made their way back to floor 1 eventually, at which point they were overleveled and just harlem globetrottersed the morlocks. It was a great change of pace after the absolutely brutal floor 2. They ended up negotiating with the spider king.
4/5. Cool lore and love the more cosmic elements. Great creatures, thematic consistency while having variety. Challenging but fair. Could use a random encounter table and more of the classic dungeon crawling resources.