In addition to multiplayer details that have been reported previously, such an association between single-player mode and multiplayer, where the success rate of players in the online mode will affect the single-player mode. Currently there are new details revealed in the Houston Mass Effect 3 multiplayer modes, such as lack of support for using Kinect in this game, and players will be able to play several characters of the races previously unexpected, like the Krogan, Drell and Asari.
For co-op feature, there will be DLC characters, and co-op campaign will have a very different story with the character in single-player mode, including the emergence of some unique characters. Later there will also be lots of customization options on items of weapons and armor in multiplayer mode, and also added some new Achievements and Trophies.
One thing that might be a bit disappointing is that there will be no support for local multiplayer, or in other words a player can not make the offline server.
Mass Effect 3 will be released in March 2012 for Xbox 360, PS3 and PC.