I like vampires, but I'm generally more into vampire folklore than modern vampire fiction. Like with dragons, elves, dwarves, werewolves, and other popular fantasy creatures at a certain point I reached the "this was a good meal but I'm full now" stage. I've seen too much of these things for them to really be novel to me as literary characters, and I find the folklore and the belief patterns behind it to be more fascinating.
That said I do enjoy such creatures on occasion, when I think the writer has found a fresh perspective on the whole thing. Dracula is a favorite novel of mine, and I think it's for some of the same reasons I like Tolkien and dislike derivative works drawing from both. Both Stoker and Tolkien were people fascinated by folklore and myth, and they poured over those old accounts of strange beliefs and primal fears, then picked and chose, keeping what they liked, discarding what they didn't, mixing in some elements of modern sensibilities, and creating something all their own. Other writers later looked at their work and just copied it with some few tweaks, which is nowhere near as impressive an effort. I find I'm mostly fascinated by authors who put in the legwork, going back to the well of belief and then trying to create something of their own out of the many contradictory traditions they find there.
And in that vein I find there's one aspect the vampires that is ripe for more exploration and rarely gets it: just who's in there, anyway?
In traditional vampire fiction, a vampire is usually controlled by the same personality that animated it in life. That's where much of the angst and drama comes from, as the person who has been transformed into a vampire grapples with his or her compulsion to kill other people and drink their blood. Some more modern takes have instead depicted them as little more than ravening, mindless monsters. Neither approach quite reflects the folklore, and I find that both interesting and frustrating, because there are dark uncharted waters there.
In folktales the creatures are not a talkative bunch. I can count the number of stories I've stumbled across where a vampire talks with a human being, or shows any sign that it remembers its previous life, on one hand. Likewise, you don't see much in the way of vampire communities. Secret vampire societies are a cliché in modern literature, but are entirely non-existent in Slavic tradition. Vampirism in folklore tends to be endemic, not epidemic, to any given society, and a vampire biting or killing someone doesn't necessarily mean they will become a vampire. Folkloric vampires are loners, and while they sometimes kill a number of people, few come back in the end, and they don't all hang out together.
Generally, the old Slavs seem to have believed it was an evil spirit that animated the vampire's corpse. Now, sure, sometimes it was the spirit of the same person, if they had been evil in life. Sometimes it was the spirit of somebody else, or a flat out demonic spirit, in which case they might use the memories of the deceased against the living.
Most often, it seems to be a foreign, hostile spirit of unknown origin. There was, for example, a tradition that a vampire could be created when a black cat jumped over a corpse, presumably hunting for the dead man's soul, since souls were often symbolized as mice in the Slavic tradition. As the old spirit leaves a horrible new one replaces it. Now some modern stuff like Buffy deals with this approach, but what's interesting is you don't often get a strong sense of the personality the possessing spirit has. It's usually just a generic kind of evil, a cackling bloodlust that doesn't give you any sense that this spirit had a history or "life" before it showed up in this person's corpse.
And even in the folklore they don't get into it that much. It's rarely spelled out that the devil or demons are animating vampires, and if that is mentioned it's fleeting and not detailed. For example, there's no tradition in dealing with vampires in the same way there is with demonic exorcisms, where you have to learn the name of the offending demon before you can drive it out. The closest I'm aware of to something like this is a folktale where a defeated vampire is burned on a pyre, only for the body burst and thousands snakes, crows, maggots, rats, etc, crawl out of the body and try to flee the fire. The villagers kill them with shovels and pitchforks and throw each one back onto the fire, as each creature was a little part of the vampire's evil spirit, and that if even one escaped it could find another body and start the cycle all over again. So an acknowledgement that vampires can be created by foreign spirits, but still no word on where the spirit originally came from or who it was to begin with.
And for the vampires that are clearly animated by the spirit of a dead humans they act more like ghosts than people, killing those they knew or loved in life for no clear reason, lingering around the places they used to live, acting out old routines, etc. It's not clear how much of them came back, or what motivates them.
I feel there's a lot of potential for fiction in all this, and it seems like it's rarely tapped into.