I picked up a copy on EBay for the sake of completeness. I'm a geek for Monster books, so had to have this one- even though I have no intention of switching to the latest "version" of the game.
I found it a mixed bag.
likes:
the layout seems very DM friendly. EZ to find hat you're looking for, and some extras to make building encounters easier.
higher level monsters got some needed buffing.
dislikes:
auto special damage attacks. No save, no way to mitigate the effect, just EFF YOU. No. Not in my game. And I'd walk from any game I played in that did it this way.
Same issue with stat blocks the last MM has: instead of giving us a straitforward way to adjust NPC's to match our parties- like 3e did- we get 3 separate stat blocks. low, med, high. I find that they rarely match up that well.
in the same vein, NPC spellcasters are really weird! I'd prefer a strait up "x level Wizard" for example, because it would be easier to customize their spells, etal. ( it annoys me that EVERY wizard we meet has the exact same spells...) Spell lists seem unusually short, too.
I have been mainly converting older adventures for play with 2014 rules. ( the hardbound 5e premade campaigns just don't fit my style... And I find them a PITA to actually work out of) Simple swaps for the current monsters, spells and items. Should be easy, right? Nope. The above nit picks make them more complicated than necessary.
The lack of core D&D monsters, like Drow, Orcs, and Duergar are a huge turnoff for me. As are a lot of the unnecessary type changes ( was a humanoid, now a fey, for example), and the changing of longstanding lore. (Dryad, I'm looking at YOU!) WHY???
All in all, I will likely not use it much. 2014+ Volo's still works great- as do the 3rd party 5e books, like Creature Codex from Kobold Press. (You want Fey creatures? Good Lord, but did they go all-in on those in the 2 BIG volumes I own, lol)