It had a lot of monsters--which is doubtless no particular surprise--with a particular emphasis on higher-level monsters.
But few of the things in the book really fit the themes of my campaign. And the ones that did seemed too powerful. The darktentacles, for example, seemed horribly nasty for a CR 7 monster. Even more boggling were things like the 'bone ooze' that's a CR20 ooze. (Yowza!)
The number of really high-level monsters bugs me a bit. I keep thinking of how they made such a big deal of the tarrasque being a unique monster--and now there are things just as tough as the tarrasque wandering around in multiples. There are even oozes as tough as the tarrasque.
Some good points: they explicitly listed flatfooted ACs and touch ACs for monsters. For monsters that used grapple checks as part of their style, it included the grapple bonuses. (Which can be serious--I noticed one monster with a +46 grapple modifier.)
And as another aside--I wonder why I haven't seen a WotC D&D 3/e treatment of the intellect devourer (I have doubts about whether that site is perfectly free of intellectual property violations.) I think of the intellect devourer and the rust monster as classic D&D monsters that had no existence before early editions of D&D.