Heres some info we know by just viewing the trailer
* Set in modern-day Liberty City (based on New York) - (Liberty City is on the back of the boat under "PLATYPUS"
* Immense graphics - millions of times better than the cartoony GTA3/VC/SA
* Realistic sky, realistic birds, much better quality cars
* Decent smoke and other particle effects
* Moving billboards
* Awesome sky effects with moving shadows
* Niko Bellic is the main character, a non-American character - eastern European accent
* Multi-player will be included, but no details yet. It will not be MMO.
* The game has been in development since early 2004.
* Variations in the terrain cause the walking animation to change. The physics have also improved and character movements are more realistic.
* Liberty City is the only location in the game.
* The Xbox 360 version was the version shown to the magazine editors.
* There were no planes in the skies of the demo that the magazine editors saw, and it seems that there will not be airplanes in the game. Other forms of air travel should not be ruled out.
* The MetLife building now bears the name Getalife, the Statue of Liberty is now the Statue of Happiness, and DUMBO (Down Under the Manhattan Bridge Overpass) is called BOABO (Beneath the Offramp of the Algonquin Bridge Overpass).
* Dan Houser of Rockstar Games said that New York City "is an environment we felt had never been done to the level we were envisioning it in a video game. From looking at all of the locations, this was the one that really stood out to us, and really had that impact. It has all of these iconic things that you couldn't put into a game before."
* Within Grand Theft Auto IV, Rockstar North has recreated four of the five boroughs that make up New York City, as well as a section of New Jersey. In the GTA universe, Brooklyn has been transformed to Broker, Manhattan has mutated into Algonquin, Queens is now Dukes, The Bronx is Bohan, and New Jersey has become Alderney.
* It's a smaller geographical mass than San Andreas, but not an inch of this world is wasted or dedicated to vast stretches of country or desert. It's a tightly packed metropolis that captures the eye with its decades of world-class architecture, sun-blocking towers, and extraordinary walks of life.
* The city is brought to life with an amazing level of realism. Sunlight glistens beautifully off of glasswork, illuminates the intricate detailing of century old brick, and even reveals just how realistic an ordinary bag of trash can look. As the sun begins to set, the city takes on a whole different appearance. Buildings that were once eye-popping attractions slowly become ominous obelisks. As any New Yorker will tell you, there's a big difference between New York during the day and New York at night. Liberty City will perfectly capture that quality.
* Niko Bellic's home is in Eastern Europe, and he likely may never have traveled to Liberty City if it wasn't for his cousin Roman. With life not working out in the homeland, "Bellic turns up in Liberty City because he's been receiving e-mails from his cousin Roman, that read like: 'I live this amazing life, it's the American Dream come true. I have two women. I have four hot tubs. I have fifteen sports cars," Houser elaborates. "And [bellic] believes it." His bid to flee his past for what he thought would be the greener pastures of America couldn't be any further from the truth. Roman has been lying to him. He isn't rich. He isn't popular. And he's actually in a load of trouble. He lied to his cousin to hide his own failures in life.
* Roman, Niko's cousin, is the only person that he knows in America. He serves as one of his main friends, motivations, and connections at the start of the game. Unlike San Andreas, players won't get a chance to see Bellic in his homeland. You will see his life unfold from the moment he steps into Liberty City.
* Niko is a "tough character" while Roman is a "friendly buffoon."
* The story unfolds in a number of different ways. R* is giving people more freedom, more choice and more sense of control over their destiny - the structure of the storyline is quite different to previous games.
* A Near Collision between two cars caused a pedestrian to proclaim loudly "That was fucked up"
* As Niko approached several people milling in a large group, he sort weaved in and out of them. At one point, he even pushed a pedestrian gently out of his way.
* As Niko continued descending a small hill further down the road, we noticed the way his weight seemed to shift backwards a little, as though he was saving himself from just pitching fowards and setting off into a run. He looked exactly like someone walking down a hill does.
* Another example of the wight shifting was shown later, when Niko began running - looking much like a normal person does instead of some unrealistic videogame representation. He leaned a little to the left and right, depending on which direction Rockstar took him, rather than his top half staying stationary and only his legs moving, as per previous GTA games.
* The sight of Niko just walking up some steps managed to impress too.
* The Rockstar team did inform us that that fire escapes and other stuff can be used within the game. We saw a ton of these around Broker and we're sure they'll come in handy, at least in terms of roof access for sniping missions i nthe finished game, if sniper missions remain, of course.
* Rather than the rags to riches story of old games, GTA IV looks more like a rags to better rags story. The idea is ostensibly for Bellic to keep afloat in Liberty City, rather than walking the streets with tons of cash dripping out of every pocket. After all, if Niko had accumulated over half a million dollars, it's a little far fetched for him to want to carry out other misisons. He'd be set for life from that point on and could provide for both himself and his brother. We therefore imagine GTA IV will have a much more realistic approach to funds and how much you'll ultimately have to spend them throughout the game.
* Little focus on building business empires this time - it makes no sense to continue living a criminal life if you're pulling in lucrative results at your pizza parlour, nightclub or taxi rank.
* Unlike other GTAs, IV will have a lesser known voice cast and music that isn't distinctly popular or obvious to the 2007 settings. Expect many unsigned bands or indies to show up.