There's a lot to like about the book, even if it falls short in a few areas. As other reviewers have mentioned, the artwork for the devils is atrocious (there's no effort at all to follow official descriptions from any era or the D&D aesthetic). The maps, however, are beautiful, even if the infinite layers are reduced in scope and the Avernus map is largely cut & paste from BG:DiA (as one would expect). The campaign itself is a railroad utterly dependent on NPCs (none of whom are particularly interesting). That said, for those who like the Hells there's a lot of useful bits to use, from locations, to creatures, and beyond. I'm not a fan of 5e's current Hellish hierarchy (AD&D's was more interesting), but the designers are limited in what they can do creatively. The Hellish dukes are far too weak (as, indeed, are the archdevils in 5e), but the scaling problem in 5e is well-known. To me this book is best used as a resource for the Hells rather than a campaign.