The best 2E 'splat' was the Complete Dwarves Handbook, IMO, followed by the Complete Sha'irs, Complete Necromancers, Complete Thieves and Complete Spacefarers Handbooks. The Complete Elves Handbook was just painful, and I say this as a fan of Anne Rice's particularly florid writing style, and the Gnomes/Halflings Handbook didn't really do anything to spice up or draw interest to the races in question, IMO. The Complete Humanoids Handbook suffered from being essentially a laundry list, trying to cover far too many races in one too-thin book.
For 3E, Complete Warrior and Complete Arcane are awesome. Complete Divine and Complete Mage are decent, and the rest are kind of 'meh.' We've had two arcane (Complete Arcane and Mage), two divine (Complete Divine and Complete Champion), two rogue (Complete Adventurer and Complete Scoundrel) and one fighter (Complete Warrior). I wouldn't mind seeing another 'Complete' for the fighters, but I think Book of Nine Swords pretty much destroyed any chance of that.
The 'Races of' books are kinda 'meh.' The Killoran are the only race I find interesting of the new ones (the Raptorans make me think, 'Hey, here's where they failed to update the Aarakocra, who are already established as being one of the creator races of the Realms setting!' while the Goliaths give me the same vibe, 'Oh look, some racial abilities and cultural details that would have made sense for the already-established Half-Ogres.'). The Kobolds being 'updated' to a PC race so underCRed as to be a joke was amusing, but the Dragonborn were far too specialized to be useful (how many game worlds use Bahamut at all, or have a slot for a race that can only worship a single overspecialized nonhuman god of extreme alignment?) and the Spellscales didn't really ignite any fires. Of the old races that got a mild updating, the Gnolls are the only interesting one, and even then the extra racial HD make them pretty much unplayable.