Well, I ordered my bro, the one I owe a Wedding/Christmas Gift to, a copy of the book since he's a super huge Crit Roll fan. (He doesn't really care about the PDF so I downloaded it instead.)
I do like a number of things in it. Especially in Chapter 6: Allies and Adversaries. And one image, in particular in that section, is legit an excuse to play as a Yuan-Ti Pureblood Echo Knight. A number of the Monsters are pretty neat, and there's one Fiend in there that looks pretty interesting to deal with. Especially if you go with one of the Vestments of Divergence that is in the book.
There's also, a Tiefling Vampire assassin of Vecna/The Wispered One. Doesn't have a stat block, but following 5E guidelines just means that you'd use the Vampire stat block and make the according adjustments.
There are some slight errors in it though: (again in Chapter 6.) An attack called Withering Touch is mistakenly referred to as Withering Hand in the traits section of the Remnant Chosen. And then in the Vox Machina section, if I'm reading correctly, Keyleth is legit helpless after casting all of her spells, with no ability to do a regular attack that uses her iconic weapon for just swinging.
Aside from those small errors, I like it a lot. Already I have ideas for using stuff from here for a horror based Icewind Dale type one-shot using the Rime of the Frostmaiden's Character Secrets and Survivors from Van Richten's guide to Ravensloft.