Jeez I hated MMIV.
The maps...waste. The encounters. Stupid. It's a MONSTER MANUAL! The increased detail...half of it is useless. I don't need to know how long a creature is in its gestation period or the color of its dung. The classed monsters just pissed me off to the point where I wanted to rip out the pages, mail them to WotC and leave a letter saying "NO! Bad designers! No! Wrong book!"
The gems were there, like the new fey creatures (I like Lunar Ravager and Verdant Prince) and a few others, even the yugoloths of course (even though the guy wrote the their names screwed up with the naming convention).
I believe it was James Jacobs, not sure exactly, but he said he wrote some of the new creatures in MMV and doesn't recall there being too many classed creatures as before and doesn't remember writing them himself.