Bad Paper said:
I disagree. IMO, the strength of the Draconomicon (well, in addition to being generally high quality) is that dragons are rather similar to one another. You pretty much know what to expect from a dragon: physically powerful, breath weapon, relatively minor magic, high levels of cunning, etc. Sure, there are differences between types, but the similarities are a lot bigger.
Libris Mortis and Lords of Madness suffered in comparison, because they had to be split up into different parts, each describing creatures that are rather different from one another. Mind flayers don't really have much in common with neogi or beholders, other than a general weirdness. I think the 2e books I, Tyrant and The Illithiad worked better in this regard, focusing on one type of monster (beholder and mind flayer, respectively) and doing some more immediate variants (various beholderkin as well as some mind flayer variations). Pretty sure the same goes for the 2e Van Richten's Guides as well, but not being a Ravenloft fan I never looked into those.
Magical beasts have even less in common with one another. That's basically the "none of the above" monster category. The only thing they have in common are the purely game-mechanical stuff.
Now, a Giant book, or a Lycanthrope book, those have potential. Or a Fey book - fey have at least as much in common with one another as aberrations do.