Along with Dark Messiah (which I still have yet to play through completely), I'd say Vampire The Masquerade: Bloodlines. Buggy as DM (using the same engine, natch) but it's got a decent story, some memorable characters, and IMHO well-implemented vampiric powers. Want to slit up your fellow man with nasty claws? Can do. Looking to move invisibly through the night and stealth-kill everything in sight? That's an option, too. Interested in being a political mover and shaker, as you persuade, seduce and intimidate your way to the top? Go for it. I've played a few of the clans and find something new every time I start over, even if the dialog doesn't always change. Some of it is still hilarious.