so far, this is what i've read up on:
Overview
Aliens: Colonial Marines is a squad-based first-person shooter in which the player controls four Colonial Marines, each with a different personality and primary weapon. Each player character can carry additional weapons including a flamethrower, pulse rifle, smartgun, pistol, RPG, and many types of grenades.
The player controls one marine at a time, issues orders to the others using context-sensitive commands, and may switch between characters at any time. The player will also occasionally be required to control a particular location, using tactical positioning and turrets to fend off attacks. Aliens: Colonial Marines will have no HUD to provide the player with onscreen information.
The primary enemies of the game are Aliens which will generally attempt to sneak up on or outflank the player, forcing the player to use tactical combat to confront them. Several different types of Aliens will appear and will attack differently. Facehuggers will attempt to attach themselves to the player character's face, implanting an embryo inside them which will then kill them. "Warrior" Aliens are the primary enemies and are based primarily on the appearance of the Alien in Aliens. "Scouts" are faster and will spy on the player characters' activities. They will work in small groups or alone. These Aliens will be based on the appearance seen in Alien. "Drones" primarily carry and position eggs and work in the heart of the Hive serving the Queen; they were originally going to be in Aliens along with the "Warriors". An Alien queen will also appear as a "boss" enemy. Quick time events will be used for one-on-one combat between the player characters and Aliens. The Aliens will occasionally flee rather than attack when confronted by more than one marine. Quick time events are also the primary mechanic when the player is attacked by a facehugger.
Multiplayer
The game will allow two players to play cooperatively on the same console, using a split screen to show the two perspectives(i.e. CoD: Black Ops). Online multiplayer will allow up to four players to play cooperatively, each using their own console and screen. Competitive multiplayer modes have been announced, but the development team has discussed the possibility of competitive online play based on the "Gloom" mod of Quake II.
Story(so far)
The story of Aliens: Colonial Marines is being written by Battlestar Galactica writers Bradley Thompson and David Weddle. The events of the game are set after those of the film Alien 3. A Colonial Marine search and rescue team has been sent to investigate the U.S.S. Sulaco in search of Ellen Ripley, Corporal Dwayne Hicks, and the rest of the missing marines who were dispatched to LV-426. The Sulaco, LV-426, and the derelict alien spacecraft from Alien all serve as environments in the game, as well as other locations yet to be detailed.
finally, to give any doubters some light, Gearbox showed 5 new screenshots at the 2010 Penny Arcade Expo. the team says that they are currently more involved in Duke Nukem: Forever, but assures us that Colonial Marines is a Priority.
and here are a few screenshots:
last word: Delayed until Jan 2013. im guessing Borderlands 2 comes first.....