I have a mixed response to this adventure. The key premise is really interesting, the creature selection is awesome, has one of the best story awards I have seen, and it has a really creative way to manage different party strengths during the body of the adventure.
It has no maps. Every encounter takes place either in a generic tunnel in the Underdark that vary only in whether they are described as 10 or 15 feet wide or in caverns that are all described with the exact same dimensions and features (except for how high the cieling is).
And there are no real role play notes. Every encounter is expected to go directly combat with no motivations or personalities given to the opponents. Even the questgiver - the only description we have of him is his title.
Then there are several of the hazards and effect which have incredibly complex mechanics with half dozen exceptions and alternatives possible, but they are not laid out in a way that is intuitive, to me at least. I had to rewrite several of them about a half dozen times until I got it to the point where it feels like something that I can adequately process in a reasonable amount of time at the table.
And finally, the whole story premise revovles around the BBEG being able to do [a thing] - which is not [a thing] that the creature's stat block allows them to do, nor does the BBEG have any magic items that allow for it to do [the thing]. It wouldn't have any mechanical effects vis a vis the players, but if the players ask, "Hey wait a minute - how did the BBEG do [the thing]???" I am left with "A wizard did it."
This has the feeling of a real diamond in the rough - with just a bit more polish and attention, this could have been a real gem. I would have given it 3 1/2 stars, but I cannot give it 4.