Usually there's some sort of redeeming features to the bad guys, but not Orochimaru, he's a evil twerp who wants to be Immortal, and will do anything to stay young and pretty. Vain bastard.
:D Orochimaru is totally my favourite character. (Well. Along with Gaara, Kakashi, Temari, and Kabuto. Never let it be said that I'm decisive.) I don't think that immortality and youth is actually the biggest part of it for him. The reason I think his voice in the anime is so perfect is that it always sounds like he's about to laugh, like he finds everything amusing. I think he wants immortality&power&c. not for their own sake but because he wants to see everything, to know everything. He wants every jutsu in the world--he wants to know it all. He really does have a playful sort of personality (when we see him right before Kakashi and Kabuto meet in Sasuke's hospital room, he's daring Kabuto to kill Sasuke--because it seems that, for him, figuring out Kabuto's mind is more interesting than getting the Sharingan). At least, that's how I see him.

Anyway, his vanity pales beside Tsunade's. :D