Well, I wrote it, so I won't review it, but:
I enjoyed writing it, but felt a bit constrained by the Quint II writer's guidelines.
My goal with Monk II was to open up the martial arts archetypes a bit further, building on some of the things introduced in Monk I.
Primarily, I did this in the Prestige Class chapter, where I introduced prestige classes themed around some popular fictional archetypes. In that chapter, there's a Jedi Knightish prestige class, there's one based strongly off Buffy the Vampire Slayer, and there's one based on the archetypal Greek Olympian. I like the way the PrCs worked out - it's also worth noting that all the PrCs are 10 level classes, as that was mandated in the writer's guidelines.
I updated and revised a few of the alternative monk classes introduced in Monk I, to bring them up to speed with 3.5, which expanded the possibilities of the Monk class a good deal. I scattered these changes throughout the book, though they are focused in the Class Path chapter at the beginning of the book, and the section on Martial Arts feat paths.
Because of the writer's guidelines for the Quint II series, I ended up writing Monk II as more of a companion piece to the first book - it can stand on its own, as the stuff carried over from book I is revisions and revisitations, but doesn't have as many alternative concepts (legendary feats, lion dancing, etc) as the first book.
My biggest frustrations with the book as printed are:
The guidelines for Career Paths are too set in stone, and don't vary enough from class to class. Monks and fighters are too different for the same rules of Career Path progression to work for both, and I wish I'd been given the freedom to match the guidelines to archetype, rather than having to constrain archetypes within the guidelines.
Actually, the writer's guidelines for all of the Quint II line are very... rigid, to the detriment of several of the classes. If Quint I books suffer from too little structure, I think the Quint IIs suffer from too much.
One of my favorite sections was taken out of the book and presented as an "article" in Signs & Portents. I wrote a section introducing flaws and benefits for martial artists that incorporated some of the physical and mental flaws and strengths that famous martial artists possessed - it was intended to be the monk class' version of the unique abilities introduced in Quint Sorcerer. I'm not angry (at all) that it was taken out and released as an article, but I do wish it had been in the book itself.
I wish I'd had more time. I ended up working 16 hour days to get the book in at deadline time - when I wrote Monk I, there was the luxury of time on my side. With this one, time was of the essence.
So, this is the author's opinion, for what it's worth.
Patrick Y.