Well, it all depends on how active the vampire is, and how much of their own power they're using, and what they're feeding on. See, a vampire doesn't need *blood*, so much as the anima--or life force--found in blood. So taking blood from a pig or a cow is less effective than taking blood from a human is less effective than taking blood from a dragon or a fey. Of course, pigs are also less dangerous than humans, and humans are much less dangerous than dragons, so it's a catch-22.
In most cases, a vampire only needs to feed about once a week, but they need to take enough blood from the victim that their victim may very well be at risk of dying, which is why most vampires feed in smaller amounts more frequently. This keeps their cravings down and gives them more leeway--an unsuccessful night isn't going to be a threat.
A vampire is effectively a walking corpse, and thus cannot get anima from the act of living *because they aren't alive.* So a vampire has to get their required anima through other means--specifically the blood of other living beings. It's basically like a nagging hunger--food and drink don't have the same invigorating properties that they had before, there's something missing in it. Blood, on the other hand, fills this empty place in the vampire, making them feel alive again.
Of course, this feeling can be addictive, so while the basic drive might be hunger, vampires can begin to crave to the feeling they get when full on anima--the vigour of life, forgetting for a moment that one is an abomination against nature itself. So it's actually rather common for vampires to feed when they don't have to simply to get a fix. However, there are some vamps who will try to keep a firm hold on their morality and cravings, and through discipline, resist any addicting properties.
Vampirism is a curse, though its exact origins have been lost to history. It's known it first emerged in the Middle East some 10,000 years ago, and spread throughout the early city states of Mesopotamia, Asia Minor, and India. Some claim it was a gift bestowed upon a powerful king who made a deal with Death himself, others claim it was created a mage trying to extend his life through grand blood magic rites, others believe it is the result of a demonic bargain, others say that the legendary Lilith spawned the first vampires, and still others argue it was a curse bestowed upon Cain for the first murder.
Regardless of its exact origins, vampirism is spread when a vampire drains the anima of a human, leaving behind an empty, hungering void where their spirit once resided. Note that anima is separate from blood, so a vampire doesn't have to drink a body dry as some legends state--but in most cases, a small bite usually isn't enough to fully drain someone's anima either. And again, it depends on the person--a mage has more anima than a normal human unless they've tapped themselves out during casting, while a psychic is a veritable fountain of anima that would take *dozens* of vampires to run dry. It's usually hard to get a read on how much anima a human has, so most vampires keep their feeding limited because the last thing most of them want is for vamps to pop up--and thus have more mouths to feed. Accidental conversions are still a risk, but most new vampires were singled out and purposely transformed.
Upon conversion, vampire loses their animating spirit, not their soul, and therefor they remain the same person they were before their death and rebirth. However, given one's new hungers and predatory instincts--usually accompanied by the revelation that vampires aren't a myth and that everything you thought about the world was wrong--it's typical for new vampires to undergo a psychotic break: becoming incredibly depressed, developing a new personality to cope, creating a new identity, becoming irrational and violent, hallucinating, and the like. The person who emerges from this could be incredibly different from who they were before--but this has nothing to do with the curse of vampirism and everything to do with humans trying to come to terms with their new existence. And it doesn't happen to everyone--strong willed individuals may be able to fight their way through the rebirth without cracking.
Vampire society usually takes these new vampires and offers them support and allies during the first few trying weeks and months of their unlife--typically including indoctrination into vampiric customs and beliefs. Most vampires, after all, view themselves as the epitome of undeath, and their transformation not as curse but a blessing--they're better now than they were before. Stronger. Faster. Smarter. Immune to disease and the rigours of aging. Most vampires view themselves as the true masters of the night, and believe that they *deserve* to be worshipped, feared, and followed by mankind--the cattle that feeds them. While this might sound harsh, it's a way to cope with the transformation: you're better than you were before, you have more friends and power now, and those you feed on aren't *really* like you anymore, right?
As mentioned, vampires have increased speed, stamina, strength, and an immunity to most diseases, illnesses, and aging. And that's just your standard vampire offerings. See, vampires are tied to blood, blood has a lot of anima, and anima is the stuff of magic. So basically, vampires are just brimming with magical energy. Indeed, most vampires learn how to harness the anima in blood towards many fantastic, supernatural ends, from enhancing their resilience and keeping their corpses moving, to controlling the emotions and thoughts of others, to shapeshifting, to spreading disease, to the powers of foresight and prophecy. With blood magic, vampires can control the bodies, animate corpses, read thoughts, inflict curses and disease, and assume the forms of bats, wolves, jaguars, or mist. And that's just the start--blood magic is incredibly diverse in its powers, and few know blood magic better than vampires.
Indeed, the whole thing about new vampires being enslaved to the one who turned them? Well, that's partially true, because of blood resonance. It's incredibly easy for a vampire to influence the thoughts and actions of one who they recently drank from. Why most victims either can't remember a feeding, or remember only positive things about it. Mind control is wickedly insidious, after all.
With great power comes great weaknesses. And vampires have a slough of weaknesses. Most well-known is their weakness to holy objects and symbols--it's not the object itself, of course, but the wielder's faith empowering them to resist the vampire. Faith is an incredible defence, and works not only against vampires, but also spirits, ghosts, horrors, fey, jinn, and demons. And while holy water and crosses might common objects of faith in the West, in other regions, it may be a holy book, or a prayer, or a sacred place (Mecca has been free of vampires for millenia now). Heck, even faith in non-religious things, such as faith in your country, or your ideology, or your friends could be enough to work. There's been recorded cases of vampires being driven back by hammers-and-sickles, so if you ever wonder where the whole "vampires are weak to garlic" comes from, just remember that people can believe in the power of anything.
Other than that, vampires are incredibly photosensitive and will find themselves burning to death under the glare of the sun or another bright source of UV radiation. While it's not immediately fatal to most vampires, it is incredibly painful, with their skin blistering and peeling away in minutes, and can usually kill a vampire in under an hour. Thus, most vampires restrict their activity to the nighttime hours, and if they must go out in the sun, they go out wearing heavy clothes with hoods, gloves, and gasmasks--letting no light through at all. It's a bit of a give away, honestly, and most vampires would much prefer to travel around in limos with tinted windows from one indoor parking garage to another.
Another common weakness is that vampires cannot enter a private dwelling if not invited in. Of course, most modern folks believe this applies to any enclosed location, but that's an incredibly common misconception: if it's a place where an open invitation is implied, like a restaurant, a courthouse, a mall, or even a church, a vampire can enter at will. Also, vampires cannot cross running water, but that's physically cross--standing at the other side of a river only works if the vampire can't find a bridge.
Also, steaks to the heart aren't fatal, but the original myths were right in that it bound a vampire and prevented them from moving or acting. So it's an effective way of binding them if you can't permanently kill them for whatever reason.
A vampire's appearance depends on how recently they've fed, and how full on life and anima they are. A satiated vampire can appear almost human--skin a bit paler, eyes a bit dull, teeth a bit more pointed, skin a bit colder, but easily passable as human. Indeed, the transformation into a vampire usually makes one appear *healthier* than they were in life: a bit younger, stronger, more attractive in many regards. A hungry vampire, on the other hand, appears almost like a gaunt, feral beast with a maw full of fangs, fingers twisted into vicious claws, clammy skin clinging close to the bone, thinning hair, shallow cheeks and eyes blazing with unholy fire. Its not pleasant, and most vampires hate being seen in such a vulgar state. Interestingly, vampires who feed primarily on animals will often find themselves taking the traits of the animals whose blood they consume, appearing monstrous despite arguably being more humane.
Because of their ability to control the minds of humans, their longevity and physical prowess, and their supernatural grace, vampires came to view themselves as superior to humanity. Indeed, a number of vampires still view humans as cattle, primarily kept alive to feed and serve their vampiric masters. Using their powers, many vampires rose to positions of prominence in human nations, and indeed many legendary despots of early human history were vampires. For several thousand years, vampires were the most powerful of the supernatural races, their influence spreading across the world. They would inflict their curse on loyal servants and allies, bringing them into the fold of unlife, and forming numerous vampiric dynasties, some of which survive even into the modern era.
As vampires see themselves as the nobility of the supernatural world, it should really not surprise anyone to know many that many dynasties keep records of their history and membership that dates back centuries, if not millenia. Indeed, one of the most powerful modern dynasties, the Romanian Drăculești, or "Sons of the Dragon," proudly trace their lineage back to Vlad Dracul--who in his afterlife is now known as the infamous Dracula. However, the Sons of the Dragon are rather unique, in that their founder is still around and kicking... most dynasties have lost their founders to the ages, and the eldest have even lost their histories