I was surprised to like this as much as I do. As others have noted, this is a high magic setting, and I generally prefer lower levels of magic. The NPCs presented tend towards high stats and most have several levels of experience in some class or the other. Since I envision even a 1st level fighter (a "Veteran") to be a superior warrior to typical militiaman, having most shopkeepers be able to outfight lower level characters isn't something I care for. Worse, most of those same NPCs have one or (more often) several magic items, and most of them are stock items (lots of swords +1, etc.) without much color or "magic" to them, which I really dislike. Finally, the proofreading on Kalas certainly leaves a bit to be desired, and it gives the impression that it wasn't written for C&C, since the SEIGE engine makes nary an appearance (NPCs don't have prime attributes provided, etc.).
Most of those things are easily fixed. It's very easy to downgrade NPC stats and levels as needed. It's also easy to downgrade those +1 magic items to masterwork items, and it doesn't take too much work to provide additional color to the rest of the magic items, making the more "magical". Finally, assigning primes is dead simple, and the lack of SEIGE engine integration serves as a left handed boon to anyone not using Kalas with C&C.
So what's left is the meat of the book, which are the characterizations and hooks. And that's where Kalas is simply outstanding. There are many, many personalities that are distinct, interesting, and engaging, making the city of Kalas feel very alive. Furthermore, the city is so rife with adventure opportunities - many of them plainly laid out in lists that follow most of the building entries - that it makes the life of the referee nearly as easy as can be. The only problem in this regard is that the book was written more to be enjoyable to read than easily useable at the gaming table. The descriptions are more verbose than strictly utilitarian. Thus, Kalas is much more useful to referees that have time to read the whole book before use than to those winging it. For what it's worth, I found the author's writing to be quite enjoyable, so that problem is mitigated to a degree.
Overall, despite the upfront investment in time that Kalas will require for it to work well for me, the seemingly hundreds of quality adventure hooks, interesting characters, and useful tables have made this a very worthwhile purchase. Highly recommended.
[5 of 5 Stars!]