Unlike most Undead (who are merely considered cursed or just plain automatons), vampires are considered heretical by nature since they, according to legend and religious doictrine, are the chosen warriors and servants of one of the surface's many disgusting gods. In this case a vile god (a male divinity no less!) of murder, parasitic feeding and tyranny.
Vampires look like humans, albeit pale of skin, in excellent physical shape. Their flesh is cool to the touch.
According to all knowledgeable sources, vampires have all manner of nasty abilities and skills, including supernatural speed, strength, senses and the revolting habit of drinking the blood of the living, thus robbing them of their life, strengthening the vampire and (gasp!) stealing the blood which is Lolth's property by right of sacrifice.