Although World of Nevermore has a brilliant and crazy aesthetic which appeals to me pretty much on every level, it doesn't nail down certain aspects of how the setting should be used and so falls (perhaps barely) short of a perfect score.
So let's talk about adventures in dreams. This is a theme in fantasy (and horror) literature for many years, and there've been many RPGs that have attempted it. The core problem is of course that waking up back in a world that hasn't been affected by the dream is unsatisfying: why attempt to overcome obstacles that are simply imaginary? H.P. Lovecraft gave his Dreamlands physical reality; Adamant Entertainment had a Dreamwalker game in the d20 era which tried a similar approach. Shattered Dreams, a badly organized 1990s game had the brilliant idea that monsters from the dream world were invading people's bodies via their dreams and a failure in the dream world meant the player characters would have to face essentially demon possession scenarios in the real world - where they had no dream-altering abilities. (Someday I want to see a dream-adventure scenario where the real-world impact of a success is "you work out some emotional or intellectual problem or anxiety that's been hammering at you in the real world"!)
It's that issue that Nevermore doesn't hit square on the head. When, if things get too rough, a significant portion of the inhabitants can simply opt out of the world every eight hours, it becomes difficult to create actual conflict with consequences. The game seems to recognize this, emphasizing that GMs should make events in Nevermore prefigure or subtly affect things in the "real" game world if the whole game's not going to be set there. However, the brief mention of it doesn't give examples, methods, or principles to make this happen - and that's frankly the most important question that I have when picking up a dream walking supplement. What about this is real?
There are even some indications in World of Nevermore that this question was not too well thought out. It is suggested (for example) that characters should retain their levels gained while in Nevermore once they wake up, typically adept levels. This could result in people in your core game world going to sleep as level 3 folks and waking up as level 18 folks one in-character day later - since time in the "real" world (whatever it is) doesn't pass as it does in Nevermore.
The simple way to handle this is to say "Nevermore's the game world. You can't opt out. It behaves in dreamlike ways but for various reasons none of you will be 'waking up'". Certain character types are like this (such as those born in Nevermore or the fey who are its original natives), a GM can simply require that all characters be one of these types.
The most important changes to the True20 system are a boosted Conviction system which allows dreamlike discontinuities to aid the characters, and an Aspect system which gives boosts to characters based on dreamlike aspects that they take on in various situations - I dream I'm a dragonlike figure, so I take on dragonlike abilities. These seem to be well-founded and since everyone in the game world has them, the balance of them seems well thought out.
The majority of the book is taken up with the campaign world description. It involves many realms, each of which has its own personality, and typical dream-effects that can be found in its borders. Probably the best part is the list of potential adventure hooks for each area. Although I'm experienced in turning area descriptions into actionable adventures, it's great to see how the tone and atmosphere of each area is intended to mesh with the typical True20 action-adventure feel. I wish every location supplement was as straightforward with what its intentions are.
Finally, a sample adventure is at the end. Again, a welcome addition to the supplement, showing me how it's supposed to be done (including what typical badguys in Nevermore get up to.)
I do think that Nevermore has a lot going for it, and it's quite ambitious; not just another game with Oz in it, thereby guaranteeing a high score from JDCorley on the Internet. However, there are certain holes in what it tries to accomplish that keep it from getting my highest marks. While the 8-hour cycle of Nevermore is terrific for keeping things changing, dreamlike and mysterious, it requires some really diligent timekeeping on the part of the GM and players, much more rigorous than in your typical True20 game, and there aren't any tools to help us do that. As mentioned above, the way to tie Nevermore to something real and worth doing is not clear.
Nevertheless the work is imaginative and thrilling, I want to adventure here and the game gives me great tools with which to do that. The abilities of player characters and NPCs alike are vivid and compelling. Expeditious Retreat hardly ever misses the mark and it doesn't here. I highly recommend World of Nevermore as an addition to your dream-fantasy library! (You do have one, right?)