CS Nation has gotten some information from the Latest "Gamer Informer" magazine which has started to arrive to subscribers. 

Single Player Details

• Stand alone, full-priced retail release
• GLaDOS and Chell return
• Portal 2 takes place well after the events in Half-Life 2
• Portal 2 takes place hundreds of years after the events in Portal
• The labs are in various stages of decay with plant life taking over many areas of the facility
• The AI cores (seen previously at the end of game cutscene in Portal) have been tasked with rebuilding the facility
• One such core, Wheatley, serves as a preliminary guide at the start of the game
• Wheatley, fed up with his rather limited lifestyle promises to aid Chell in her escape if she helps "him"
• Wheatley will be carried through some of the earliest areas of the game and can be used to open various areas of the lab to bypass obstacles
• Chell encounters GLaDOS rather early on in the game: "Oh, it's you. It's been a long time. How have you been? I've been really busy being dead. You know, after you murdered me? (...) Okay look, we both said a lot of things that you are going to regret. But I think we should put our differences behind us. For science. You monster.
• Chell no longer sports the orange jumpsuit
• "Vital Apparatus Vents" are tubes with strong suction that Chell can use to her advantage. Place one portal at the suction area and another near some debris that needs cleared and a vortex of objects is sucked out of the room through the portal.
• Tractor beams are new and can be used to help Chell reach otherwise unreachable areas
• "Projected bridges" are translucent bridges that can be redirected through portals
• "Paint" has been added and does react to the physics of a portal
• Orange paint rockets Chell at high speeds
• Blue paint acts as a trampoline like substance and can even be used to coat cubes to send them bouncing around
• Aerial Faith Plates act as spring boards to send Chell flying
• Redirection cubes have reflective sides to bounce laser beams at angles
• Weighted Storage Balls
• Due to the state of the facility, GLaDOS is often forced to send you behind the scenes of the test chambers to make your way to the next area
• Erik Wolpaw, Chet Faliszek, and Jay Pinkerton (National Lampoon) are the main writers on Portal 2
• Music will play a bigger role this time around. Players will find new songs throughout the game through various means.
• Jonathan Coulton will be involved

Multiplayer Details

• Separate, full-length co-op campaign
• Play as one of two bipedal robots
• One is made of a personality core, the other is made from a turret
• Each player will have a portal gun (yes, four portals at once) with either player able to use the other's portal when needed
• Either split-screen or online play with a picture in picture option to see what your partner is doing
• Co-op maps will be more difficult than the single player maps due to the nature of communication and bouncing of ideas off of partners