Four things:

1. I expect a compendium to be a summary of a subject. This book is primarily a bestiary with a decent number of powerful fey NPCs at the end. I would have like to have seen more about some of the places such as Astrazalian, brokenstone Vale or Evereska.
2. The book doesn't seem to be coherent, but rather a dump of a lot of information
3. The information needs more organization;Appendix A is useful but not enough. More importantly, an example of how to use all of these in an coherent adventage would be helpful.
4. The book needs a lot of editing:

Page 8- Next to the 'Fey Magic by CR' there is a paragraph that is mostly cut off. The same sort of thing is true for pages 196 and 197. Page 13 There's are sentences that are cut off "In this cosmology, the demesnes of Tír Naofa and Hagsend are not simply locations on Outer Planes, they are", "In this alternative model, any archfey can access" Page 35- I suspect that duicraft should be druidcraft. Page 44- spys should be spies. There are a LOT of grammatical errors, senteecnes without periods, missing commas and the like.

Even given all that, there's a lot of information to mine and it would be quite possible to put together a campaign using this information... but you'd have to fill in a lot of the blanks.

This author is amazing at what they do in numerous ways!

First, the quality of the statblocks, lore, and all around cohesion of this product (especially when taken in conjunction with the other books in the series) is astounding. I could only WISH to be as well-read and inspired as this author is.

Second, the author CARES. I submitted an issue I had with the scans, and the author had it taken care of and updated within the day.

Third, I feel confident in this author's ability to design encounters. Even if I theoretically have to balance something on the fly (which I doubt would be the fault of the content on display here), just going through these entires makes me feel confident that I'm on just as solid ground as if I were using a WotC-published book.

If the above hasn't already spelled out the obvious, I cannot recommend this book (and its series) enough.

The breadth and depth of lore in this (and all the author's fey products) is astounding! I appreciate the tremendous time and effort that must have gone into incorporating both real-world tropes and legends and settings and characters from the long history of D&D products - and I'm beyond delighted that someone has saved me the work of trying to convert 2e/4e statblocks myself.

The content is rich and thematic enough (in an area that's gotten very little official 5e attention) that I can't bring myself to subtract any stars, but caveat emptor: this supplement (likewise "Lords and Ladies," so far the only other entry in the author's fey series which I've read closely) would benefit from some further copyediting. Most of the errors seem to be of the c&p variety and don't significantly obsure the author's intent - missing Passive Perception scores, archaic names for spells, that sort of thing. If you're moderately practiced at reading and using statblocks, it shouldn't give you too much trouble, but I'd recommend giving any monsters you want to use a close read before running them.

This serves as a good base for better fey in your game. The fey are among the least developed set of creatures lore wise despite having the most real world lore. This serves as a good base for adding more fey to your game.

This compendium is amazing. A wealth of knowledge of the fey, and perfect for a campaign. The quality of the content is A+. Highly recommended.

I love the content in this supplement, and have been using the lore and creatures in my current sessions. I would recommend this to anyone looking to make Fey a major part of your story or subplots. I would rate this 5 stars, but the supplement is riddled with typos that really make it hard to understand sometimes.