Although I thought the Creature Collection was somewhat flawed (and thus only average) I eagerly picked up it's sequel, Creature Collection II: Dark Menagerie partly because I so love monster books, and partly because the first book had a few really neat ideas that I hoped SSS could follow up on. The second book has even less in the way of non-monster material than the first book did, although it does feature an appendix of monsters by CR that features all the entries from the Creature Collection(s) and the Monster Manual and revised monster summoning tables.
A major gripe I had about the first book was the spotty art. In my opinion, this has vastly improved for Creature Collection II[/green] even though Ron Spencer didn't return and Jeff Rebner's work is reduced as well. Luckily the artists I didn't like didn't come back either, and in general, the rest of them stepped it up a bit from mediocre/OK to better than average, at least. It's not all wonderful, of course, but it certainly is competitive, at least, in this regard, with other products by other groups.
The creature concepts seem to be better as well. The Carnival Krewe, unfortunatly, gets a few more members, but other than that, I thought the concepts here were more consistently solid than in the previous book. Some great new outsiders --demons, devils and daemons -- all make their appearance, and work well along with not only the standard ones in the two Monster Manuals but also the more edgy stuff produced by Green Ronin, for instance. A number of clever animal-like creatures that are easily portable to most any setting are found throughout -- I know of at least one Kingdoms of Kalamar campaign that regularly uses spined lizards, for example. I've also had great fun throwing setting-neutral things like tar golems at my PCs (watching them get their weapons stuck in his body was priceless, and of course they fell for the trap of trying to set the thing on fire!) Some of the really clever ideas, which are also fairly portable, include the haglings -- children that are taken and corrupted by hags into hag-like creatures themselves, the wicker-man -- a classic concept done very well, all new ratman (yeah!), the arcane devourer -- a strange humanoid that steals arcane spells from your casters, the absolutely revolting carrion hound -- a dog with "heads" that are giant writhing maggots, and the pisceans -- sort of like aqautic ogres. Just to name a few highlights!
There's also some clever templates in the back -- really unique ideas, like the conundrum creatures that are shattered into a number of puzzle pieces, and can only rebuild themselves by having their riddles answered, or the hex creatures, creatures tied to hags as their bonded servants.
All in all, this was certainly an improvement from Creature Collection although it still has its share of bland or mediocre concepts (but what monster book doesn't, with the possible exception of the Monsternomicon?) and some of the artwork is still not as good as, certainly, other pieces within this same work. Some of the monsters are also not as portable into other settings as others -- being quite intimately tied to the Scarred Lands setting. Although interprising DMs can do a lot on that front, and luckily these creatures are relatively rare -- a little change in some background and history and the mechanics and look, at leats, of most of these creatures are still good. Because of these issues, the book certainly isn't perfect, but it's above average, so I'll give it a 4.
While it's hard to single out a favorite, I would say the Pisceans and the Quicksilver Stalker rank very high in terms of my favorite types of Humaniods and Abberations. 
