Volo’s guide to monsters is for the most part the monster manual two of D&D 5e. this book though goes beyond just being a typical monster book though as the first third of the book goes into great detail on several iconic monsters of D&D including the beholder and the illithid. there is also a section on new player races such as the orc, firbolg, and kolbold.
I do enjoy the extended ecology’s section of the monster manual as it really fleshes out the monsters in that section. I particularly like how there is even a sample city for the races that can be used when there is no time for map drawing. one of the things I dislike is the new player race of firbolg, now the race as they have it is great, but it is not a firbolg of the old days of D&D. the 5e firbolg is closer to the old wood giants of prior editions in terms of background and stats. also the whole no names thing is so very stupid. how are you going to have a people with speech and rational thought without names. i can see it now a tree is about to fall on fribolg A and another firbolg be like hay you other firbolg friend a tree is falling look out. even worse is in lieu of names they supposedly use descriptions for identifying. so in the above scenario is would be like hay person who is male with the brown hair, blue nose and who has a third nipple watch out.
there is also several cool buffs on old races in the book. for example each giant has stats for a giant champion of their god, which is often a very beefed up version of the base giant.
the art and layout of the book are amazing as is to be expected with the number one rpg company in the world. now this book is not needed at all for playing 5e, but it does add many new monsters and more detail on some of the classics, so if you are going for another book to add to your 5e game play experience add this one you will not be disappointed.