Vampires and games about them have been done before. First-person shooters have been done before. However, I would say that Vampire Rain - a first person shooter about fighting vampires - is a reasonably innovative combination of these elements.
The story revolves around a new special forces unit made to investigate the millions of disappearances that had been occurring, connected with the appearance of "nightwalkers" - a kind of cross between vampires and zombies. They've got the "no sunlight", "really strong and fast", "hiding in plain sight", and "drinks blood" thing of vampires combined with the "turn victims into things like themselves", "hive mentality", and "rotting flesh" of zombies. The player is John Lloyd, a soldier who is part of a four-man anti-nightwalker team.
The gameplay involves a few different elements. Stealth is important, though it consists of staying out of your enemies' lines of sight (you get a "warning" of sorts if you're close to being detected). There's also a lot of crawling up drainpipes and ladders to get to the top of buildings in order to avoid detection. The emphasis is on avoiding fights more than participating in them - you're trying to reach the brain that controls all the nightwalkers, and killing it will kill them, so there's no real reason to kill any individual nightwalker.
You have a couple different gadgets, too; besides standard equipment like guns and nightvision, you also have "necrovision" that points out any nightwalkers that might otherwise blend into a crowd. Scanning any target with necrovision shows you their line of sight, which is of course helpful for a sneaking game. Necrovision can also be used to illuminate targets for snipers - if they know who's a nightwalker without the nightwalker knowing they know, the sniper can take it out free of worry or counterattack. Besides snipers and other combat support, the other use of teamwork tend to be Splinter-Cell style "I'll boost you up, then you pull me up" moves to get up on rooftops.
The nightwalkers themselves look like humans until they attack, at which point they turn into a muscular-but-rotting form. Certain weapons are better against nightwalkers than others - the pistol, for example, doesn't do anything to them except irritate them. In fact, unless you have your entire team firing at one, it's pretty much not going to go down. Pretty much any nightwalker can kill you in two hits, and even if you get the drop on them with a ranged weapon you rarely have enough ammo to take one down before you have to reload. So, in this way, it differentiates itself from Metal Gear Solid or Splinter Cell in that even if you sneak up on an enemy you can't really kill it - it's more about avoiding. In fact, that's one of the annoyances that's in this game - you're supposed to be loaded up with "anti-nightwalker" weaponry, but you can barely kill one even as a group. Thus, the stealth sequences tend to be more about survival than about defeating the enemy - hiding, sneaking, and avoiding your enemies instead of fighting them. Only until later in the game can you even hope to deal with the nightwalkers.
The game has multiplayer - the nightwalkers against the humans, with a couple of different rulesets for how death is handled (either regular death or with dead humans turning into nightwalkers. There are also 2 bonus levels that are downloadable for free from the Xbox Live Marketplace.
The graphics in this game are pretty good. The city is blanketed by both night and rain (as befits the title); the explanation for the rain is that the unit moves when it rains because the vampires' senses are reduced. The rain is well illustrated and smooth-looking. The heads-up display is the main problem with the game - the bars look bland and boring against the game's environment, and just look like there wasn't a lot of effort.
The negative aspects of this game include poor control, difficult combat, and a low quality of "horror" - basically, there's no suspense. Sure, you'll get killed if you get close to the enemies, but by the fifth or sixth time that a vampire has taken you out in two hits you won't really care anymore. Other than you, the main victims are people either grabbed or lured by the vampires into alleyways, where they are attacked. This kind of thing is sort of cliche for games (the screaming victim dragged into a hole who can't be saved). The stealth isn't very good, either, but again that's due to poor control more than anything. Your character doesn't ever handle particularly well, and considering the acute senses of your opponents this is less than helpful.
As a whole, this game gave a good try, but for a lot of reasons I didn't think it was enjoyable to play. It took a lot of elements from other stealth games but basically turned it from "you're a secret operative who uses stealth to take out enemies" to "you're a secret operative who hides from your foes so that they don't devour him". It just wasn't a very impressive game to play.