Here are some bullet points off of a couple GTA fansites (GTA4.net, GTAgaming.com), for those unwilling to sift through all that text:
Once you die and end up in hospital, you receive a text on your phone offering you to retry the mission.
Only one island (Broker/Dukes) is unlocked to begin with. The other areas are blocked with police blockades. The second area (Bohan) will open up “sooner than it has in previous GTAs.”
Vehicle GPS systems will show you the path to take in order to reach your objective. The path will be recalculated if you go off course. Fancier cars have voice navigation.
“In reaction to the crash, a lady bystander started cursing out the two men as they got out of the car, at which point the passenger drew a weapon and gunned the lady down—to the genuine surprise of all those viewing the gameplay.”
The 360 build is brighter and has slightly more vibrant color while the PS3 build has less aliasing issues.
There are eighteen radio stations in total. One is called The Vibe, which is RNB and soul. The other genres on offer include funk, reggae, jazz, dance, modern Jamaican, pop, hardcore, hip hop and a specific Eastern European station.
For whatever reason I almost always restarted every GTA any time I mission failed or died rather than go to jail/hospital. If you caught it at the right time it was faster to do it this way anyway. Will this be prevented and/or less necessary with IV?
Everything I’ve seen in these previews makes me less interested in GTA IV. They’re introducing a “hotwiring mechanic”, which basically just makes getting into a car more annoying, they’re removing all the taxi, ambulance and other random missions because they were “unrealistic” and replacing them with what sounds like scripted side missions. Overall, less “do what you want” and more “do what you’re told”. Which is sad, because it just seems like Rockstar have no idea what made GTA III a great game.