You're gonna wanna read this.
I had gotten the Kobold Press Tome of Beasts a while back after being short on monsters to use in one of my very long campaigns, and boy did I need it more than I thought. It added quite a few fey and interesting devils for my use, which was important at the time, and I was happy! 9/10
I got Volo's guide from Wizards of the Coast not long after and just about the opposite happened with me being fairly disappointed in the fewer monster options... The player options were fine and the few monsters in there were cool but I didn't have use for the overly heavy inclusion of lore at the beginning of the book since I run homebrewed games set in my own multiverse... 7/10 (solid C+)
Now I was lacking in some other things I desperate had been searching for, and trying to grab from homebrews and on the dmsguild... undead, demons, and some of my old school favorites such as the krenshar, nightshades, and other such dark entities to fill my dungeons and shadowy corners with.
The Critter Compendium sounded good... the table of contents looked interesting but there wasn't any sort of visual preview of any of the monsters so I got a little bit nervous. I read about there being things like a small section to cover more and less powerful elementals, which was something my players had desired for a while. A wider selection of beasts in appendix A sounded nice, as did monster stats and weapons for players and loot. I decided to take a chance and get the book based on a couple of nice things people had said in the comments and from what I was reading.
-I can tell everybody that for $15 this book FAR exceeded WotC's own Volo's guide as far as monsters goes. If you want dark, interesting, gritty, or even just weird or useful creatures I 100% recommend this product. When it comes to 5e this is the best monster manual I own as I'm writing this outside of the actual monster manual.
TL:DR review: 10/10, love this product.