I've only had a quick skim of the book so far but it seems pretty solid with one exception. Chapters 2, 3 and 4 seem to be in a weird order to me. Given that the Celestial Menagerie has just tried to ruin one of there shows I'm pretty sure every group i've DM'd for would jump straight to trying to getting revenge on the Celestial Menagerie rather than going on a dungeon crawl beneath the city for nebulous reasons. There doesn't seem to be much reason for the players to prioritize that over revenge on the group who just attacked them.