The new PSM article has been summarized for your conveniance in an easy-to-read bulleted-list. It covers all of the new features and confirms some of the speculation.

• The necessity of a PS2 dual-layer DVD is confirmed
• Los Santos is on the lower east side of the map and is only a small part of the state’s geography
• There are 16000 unique objects in the game as opposed to Vice City’s circa-5000
• Despite the map’s size it’s all quality, no True Crime level detail here
• No breaks during driving over bridges or into different cities, only a short second pause during the entrance of buildings
• Weilding two weapons at once is now confirmed
• Vinewood is San Andreas’ version of Hollywood
• Lots of new outfits are confirmed
• You can improve your character’s skills, such as shooting and driving
• New graphics engine confirmed (35-50% more polygons on screen at a time) including real-time reflections, a better draw distance, an enhanced shadows system and lighting effects, more detailed textures and realistic animations
• Manhunt-style gun targeting system
• Vehicles now rust and show age
• The difficulty setting automatically adjusts according to how well you do
• Not only can you improve social skills and relationships, but you can acquire a small crew of thugs that you recruit by yourself
• You acquire actual possessions
• The Flats and the Ballas are two confirmed rival gangs
• Latin flavor is added to the mix with the revealing of Cesar as a new Hispanic character
• There is an unidentified fat thug (as indicated in a screenshot) that might be a part of “the help”
• The first three missions are named “Menace”, “Driveby”, and “Reuniting the Families”
• Our first glimpses of in-game dialogue show no sign of some essential street slang, but doesn’t forget to use the word ‘homie’ nine times