Sauron's predecesor (corrupter and liege-lord too, actually) had much more substance to him, I'd say. Morgoth's brand of evil has some motives to it, although his actions strike me as just bratty rather than malevolent. ("Daddy Eru wouldn't let me mess up the music, so I'll go and kick down my siblings' lamps and trees!") In the Silm, Sauron has a bit more character -- he seduces Ar-Pharazon into corruption and an insane endeavor, after all. But in LOTR? Yikes. Boring, boring Dark Lord.