Here are some recent details that have been released on GTA IV gameplay.  Enjoy!

Single-Player
     No player customization other than clothing.  You’re stuck as Niko Bellic.
     Liberty City is modeled after modern day New York and is broken down into 4 sub-     areas.  Broker, Dukes, Bohan, Algonquin, and Alderney.
     Up to 100 Hours of gameplay (woohoo!)

Multi-Player     Supports 16 players.
     Various Modes:
           Race - Players race from one point in the city to another using 
           whatever vehicles are available.
           GTA Race - Race mode with weapons and foot races.
           Team DM - 2 to 8 teams battle to take out opposing teams.
           Hangman’s NOOSE - 4 players escort a crime boss while dodging SWAT.
           Team Mafiya - 2 to 8 teams take contracts to steal cars, or escort men.             
           Team Car Jack City - 2 to 8 teams race to steal marked cars on the map.
           Turf War - 2 teams fight to control capture points for money.
           Cops N Crooks - Two teams, one is the crooks charged with escorting their 
            boss, second team is Cops trying to kill them.
           Co-op Campaign - A smaller co-op campaign that isn’t as large as the single
            player campaign.

We are wondering if the co-op campaign is even going to be worth playing.  What do you think?