Magic of Incarnum. I like the idea of Epic, but the Epic Level Handbook has all sorts of misdeeds in its execution (and I drastically prefer my own epic BAB and saves rules). All of the Epic feats have been redone, better, in the Complete splats. It's best as an Epic Monster Manual, which is really not a good sign.
Magic of Incarnum, though, I thoroughly like. OK, that's a lie. The rigidity of alignment with the classes strikes me as a bit silly and two of the four presented races I hate (the "oh, I'm human but with scales on my neck / oh, I'm human but with spines on my arms" guys). But the mechanics are nice, the compatibility with pre-existing classes (like feats and PrCs) is very nice, and the totemist is gold.
Demiurge out.