Naturally, with more realistic everything comes more realistic bloodshed. Overall, the violence straddles a fine line between being cartoony and really disturbing. Often, the carnage is just as hilarious as it's ever been, particularly if you hit someone with a car (which usually sends them flying) or are sent skipping like a stone across concrete after someone detonates a rocket near you.
Other times, however, characters react in brutally realistic ways to being hurt. If some random pedestrian takes a couple of stab wounds, for example, they'll often try to stagger away, doubled over in pain. Meanwhile, blast a SWAT (sorry, "NOOSE") officer as he's running for cover, and you'll see him stumble mid-run, clutch at his wound and crumple to the pavement in a way that's almost guaranteed to make you wince. Sometimes, the violence can actually be hard to watch - there's no real gore or dismemberment, but the game does do some gruesome things with spraying blood, particularly during the tense, unsettlingly personal execution scenes.
It's important to stress, however, that this doesn't make the violence a total turn-off - it's just a lot more intense than the cartoony antics of San Andreas or Vice City. If nothing else, maybe the gruesomeness of the more graphic kills will give you pause to think about the meaning and the repercussions of what Niko's doing - which, as it turns out, is a central theme of the game.
At the heart of GTA IV is Niko himself, a literally fresh-off-the-boat immigrant from the Balkans (we're never told exactly where, but Serbia is heavily implied). Niko's resilient and likeable, with a sarcastic, world-weary sense of humor, but his past is filled with things he's ashamed of. He's come to Liberty for a fresh start, which he intends to get by moving in with his rich cousin, Roman. Thing is, Roman's not rich so much as he is a compulsive liar, and his gambling habit has put him on the bad side of a bunch of loan sharks, prompting Niko to intervene. His decision is the first step in a long downward spiral through Liberty City's criminal underworld, as Niko gets sucked into doing jobs for a broad assortment of very bad people.
We say "downward spiral" because GTA IV is a dramatic departure from the rags-to-riches tone of previous GTAs. Its story is darker, bleaker and much grittier, and it might lead you to places that you're not entirely comfortable with. GTA IV doesn't glamorize crime; instead, it presents a violent, more or less realistic look at the ambitious - but ultimately hopeless - lives of career criminals.
Put simply, the game is a lot of fun to play, but it doesn't look like a fun life to lead. Although they're charming and endlessly entertaining to be around, Niko and his friends really aren't much more than desperate lowlifes, living hand-to-mouth and continually dreaming of making it big. But we can see what the future holds for them just by looking at the game's older characters; best-case scenario, they'll probably end up as burned-out junkies and sociopaths, no closer to grabbing the brass ring than they were in their younger days.
That's not to say this is some bleak cautionary tale, of course - it's GTA, not Reefer Madness, and as such it's tightly written, compelling and ultimately pretty satisfying,delivering plenty of sharp social satire along the way. Niko, for his part, is a great main character - flawed and haunted, he seems obsessed with money, but really he's just trying to protect his compulsive-gambler of a cousin. He also prides himself on being "honest," which doesn't mean much in his line of work, but at least he's not an opportunistic backstabber like some of the people he'll work with. Just don't expect him to end the story as King of Liberty City.
All of this story nonsense is a lot more important than it was in previous GTAs, because GTA IV is as much a simulator of Niko's life as it is an anarchic crime game. You won't have to keep him in shape or watch a "hunger meter" this time, but you will have to manage his friendships, find him women to date and help him write e-mails to his mother. You'll also be charged with making occasional moral decisions that shape the course of the story. Some of these are simple kill/don't kill choices, but others are a lot more morally ambiguous, and it's often unclear which way is the "right" way (although some choices yield better rewards than others).