Ok, so this came in last Friday and I have to say that I’m pretty favorably inclined to it. I’m not even sure that I care about the extra monsters stat blocks, at this point I seem to be more inclined to grab my 1e books and adapt things on the fly, or I’m using modules and doing the same thing. But, the monster lore and character races are really nicely done – even the bits I will never use.
Beholders – don’t have them in my world, so not a thing for me, but still a nicely done section. I don’t have standard giants or an Ordning in my world so this is probably the least useful section for me. Yaun-Ti are the basis for my Ithians, and it was nicely done.
I don’t have Mind Flayers, so this is less useful to me but like beholders I things it’s well done section. My Ichneumon Vorre are essentially my version of Illithids, so over the years I have ganked some bits and pieces for them. The Goblinoid and Orc sections are similarly iffy, but mostly because my goblins are more Harn-esque than Tolkien in many ways, but I plenty of stuff there than I can use.
Kobolds and Hags are kind of interesting. I have kobolds, but as jungle-dwelling or desert-dwelling creatures (two differently adapted relations, the same with lizard men) but I liked the write-up. Hags as an organized group really gives me some food for thought – not sure if I’ll use it, but it’s well done.
The PC races would all need to be tweaked in the same way that I’ve tweaked the “standard races” but I like them. The new Aaismar is much more evocative than the version from the DMG, and the rest have their interesting aspects that are worth looking at.
Worth it as a GM (though perhaps not if you are a player), especially if you playing in a standard 5e setting.