[Add an IMO to the end of every line.]
Favorites;
PHB II - best new classes, best new feats, some cool new ideas, a breath of fresh air
Draconomicon - first and best of all monster splatbooks, the others knew they were beaten before they even started
Really good;
Unearthed Arcana - awesome variations, all optional, many fun
Heroes of Horror - coolness all around, and the two best new core classes outside of PHB II
Libris Mortis - very cool, loses only a few points for that creature progression nonsense from Savage Species
Dragon Magic - lots of interesting dragon-themed concepts, such as draconic pacts
Complete Arcane - Warlock, the most *novel* new core class of all the Complete books (up there with the Tome of Magic classes, but, ironically, more generally useful)
Complete Warrior - hard to beat, lots of cool PrCs and feats, hampered by a sad, sad Samurai attempt
Arms & Equipment Guide - best 3.25 book
Oriental Adventures - if this book was set in Kara-Tur, it'd be up in the favorites, instead WotC set it in some other companies setting that they've lost the rights to use. Genius!
Honorable mention;
Complete Mage - for the Reserve Feats, once again taking a concept introduced by a 3rd party publisher (that called them Locus Feats) and turning it up to 11. That's what an OGL is for, tapping the vast creative market out there to find out what we want and give it to us!
Expanded Psionics Handbook - for making the Soulknife a core class, and an interesting one at that!
Kinda hated;
Races of Whatever - meh, each and every one of them
Book of Nine Swords - for trying to make D&D into Exalted
Epic Level Handbook - for taking the game to ludicrous speed, and failing to do it well
Savage Species - for not quite getting it with the LA thing
Magic Item Compendium - for making Christmas Tree Syndrome a selling point
Dieties & Demigods - Cthulhu has no need for these 'statistics' you speak of, and Euclidean dice will not avail you in any event...
Magic of Incarnum - interesting concept that was missed by
this much, leaving me hungry for a book that takes the Totemist concept and expands it to Animal Totemists and Dragon Totemists and Undead Totemists and Elemental Totemists and Outsider Totemists, 'cause Magical Beasts, as a theme is kinda like 'every bizarre freak monster that doesn't fit in any other category and isn't quite hideous enough to call an Aberration...'
Heroes of Battle - for not being a patch on the rump of Heroes of Horror, and for introducing an interesting sounding Commander Rating mechanic that isn't actually available to use in game by any class that I've yet found...