This game is--at its best--engrossing and exciting. The characters and atmosphere grow on you.
Caine, the same Caine who murdered Abel in biblical times, is supposedly the father of all of these western vampires. He started what started the distinct bloodlines. You play as a vampire fledgling, and you are forced to take orders from a power-hungry vampire Prince, the one who's currently in charge of the vampire world in LA. As such, you can expect to do a bit of dirty work for your boss.
At the character creation screen, you will be able to select a bloodline or clan that serves as your traditional RPG "class." There are no customization options or features of any sort, though you will promptly be introduced to the stats system in this game. Stats in this game range from basic attributes like dexterity and strength to skills like computer hacking, charisma, seduction, dodging, perception, wits, firearms, and even clan-specific disciplines (powers) that are unique to your clan.
Gaining XP points and spending them on upping your skills is the primary way to up your skills, while skill books and manuals can assist. These can be bought or found.)
Curiously enough, and conveniently enough--you do not gain XP from killing other supernaturals and humans. You gain XP from completing quests; this works best because depending on which clan you are part of, you will (most of the time) be restricted to a certain play style.
(Let us say that you play a Nosferatu clan member. Would it be fair for other players who don't rely on stealth to gain levels faster because they charged through most of the game with guns blazing? What if they killed everybody but used four blood packs and you completed the same mission masterfully? You understand the point.)
This is also related to social play styles and non-melee play styles. You can be the guy with high persuasion and seduction skills, or you can be the girl with the guns. Though it is officially recommended by the game to use blades against supernaturals, you can shoot or talk or punch or sneak your way through a group of enemies.
AND OF COURSE...the bloodsucking. Blood is your MP in this game; you have both a health bar and a blood bar. Clan-specific disciplines require blood, and you can replenish your blood at any time by pressing 'f' to feed on either innocent victims or combatants. Just be aware of your "Humanity" level. If you suck people dry and kill 'em too often, you'll end up with a very low humanity level, and this increases your chances of going into a frenzy. If you have no blood and you're hunry and inhuman, you will lose all control of your character and he will run 'til he finds the nearest blood source.
If you are still interested in this game, then you should know that it runs on an earlier build of the Source engine, and it is riddled with bugs. At this point in time, however, the modding community has released its own unofficial patches. Install the patch and you'll have a completely bug-free experience. The visuals are average and nothing to complain about, so don't worry if you thought you wouldn't be able to stand 2004 visuals.
Oh, and don't break the Masquerade. The Masquerade is all about disguising your kind and hiding yourself from humans. You get five chances in the game, and if you break the rules enough--you'll have vampire hunters on your ass.
Stay sharp, newbie.