I recently purchased this book, and I highly recommend it to all Dungeon Masters. The official Monster Manual from WotC is a great resource, but in a world where magic is commonplace, there are so many more crazy creatures that could exist beyond Dragons, Orcs, Goblins, and Beholders. This book features great art, unique and innovative creature abilities, and a fantastic section in the back on NPC stats and PC options.
However, there are certainly a few hiccups in the book, and although many of the other reviews go into the countless positive aspects of the book, I wanted to touch on a few negatives.
First, though the monsters are varied and unique, not every description lines up with the artwork. I completely understand if an artistic interpretation changes the final visual design of a monster, but it's a bit irksome to read a monster description to a group of PCs and then show them a picture that looks very different. The Koralk Devil is a particularly noteworthy example.
Second, many creatures have abilities that increase or decrease ability scores, either for themselves or the PCs. Now, stat damage is excellent and should have a place in D&D, but within the core rulebooks it is limited to very few creatures and spells. No poison or disease listed in the DMG deals stat damage. If a "Wish" spell reduces a PC to 3 STR, it strains the idea that a CR 2 beastie could be able to do the same. Incremental stat damage (1d2 STR damage? Not worth it...) could easily be replaced by a disease that imposes disadvantage on that stat, much like the reverse of the "Enhance Ability" spell. Additionally, several monsters (such as the Behtu, Dogmole, and Hulking Whelp) have abilities that change their stats. Again, this ability is perfectly understandable and has a place in the D&D world. However, the text merely states that the ability scores have changed, instead of commenting on how HP, attack rolls, and damage are affected by such changes. This doesn't have to be much. HP: 22 (or 56 with ichorous infusion) would have been excellent. Looking into the rules for adjusting these abilites requires some extra work for the DM that would have been easy to remedy in the text.
There also seems to be an issue with CR on some of the creatures. The creatures don't seem to have a consistent CR with the damage output and HP indicated in the DMG. For example, the Dogmole (Offensive CR 2 and Defensive CR 1) averages out to 1.5 and is listed as CR 1, but the Eel Hound (Offensive CR 2 and Defensive CR 1) averages out to 1.5 and is listed as CR 2. Comparitively, the Giant Boar from the MM (Offensive CR 2 and Defensive CR 1/4) averages out to 1.125 and is listed as CR 2. As a DM, this would actually be what I would prefer - rounding up on CR to make monsters seem a little stronger than they actually are. This not only lets me set a better difficulty curve as an encounter designer, but also helps control PC abilities such as Turn Undead and Wild Shape. Why would any druid turn into a bear when the Dogmole is so much better? Additionally, all the new abilities, while technically cool, are often without equivalent in the DMG ability table. Some seem a bit over- or under-powered compared to the CR listed for the monster. I'm not sure some of the abilities were playtested as much as the designers claim. For example, the Eonic Drifter can completely remove a PC from combat for 1d4 rounds. Twice. At CR 1.
And that leads me to my last point. Several of the monsters have abilites or attack rolls/save DCs that don't function correctly according to the rules for monster creation listed in the DMG. For example, the clockwork abomination. With a 21 (+5) STR and a CR of 5 (+3 prof bonus), how does it have an attack roll of 9? How does it deal 1d6+6 damage? Why does its proficiency in stealth use a +3 but its proficiency in athletics and perception use a +4? And where does the saving throw DC of 14 come from? It has no stats that give the +3 bonus necessary to use that save.
Granted, these problems are relatively small, something that a talented DM can work around or a newer DM can safely ignore. However, for designers who have worked with WotC before, I am surprised that the technical accuracy is not up to the same standard as the WotC MM.
Overall, this book is a masterpiece of creativity and monster design. I'd be fascinated to see a Midgard source book released for 5E that fits with all of the amazing fey, desert, and clockwork creations within these pages. And the various Fey royalty, Arch-Devils, and Demon Lords are just begging to be used as world-threatening bosses, and they come with a few excellent minions apiece!
Again, this is an invaluable item to any dungeon master. I will be making some changes to the monsters when I use them personally, but DMs who are not as stuck up about design can and should make these monsters their own.
