Well, I started the players waking up in coffins as vampires.
DnD vampires are much more fun as PCs since they have all the traditional restrictions - garlic, holy water, invite, mirrors, running water, sunlight...
Also, starting with just blood drain + ability boosts gives a pretty good image of a newbie vampire...
Not much horror for the players, though, but they're enjoying the game quite a bit.
I always thought about doing something similar to that, kind of like Soul Reaver in tone--everything around them falling apart and them having such limits. How did it go?