This extract is taken from the official Gears of War Xbox site. An announcement on the site reads the following:

“Gears of War: Judgment” delivers the most intense and challenging Gears of Wargame yet, with a campaign that takes you back to the immediate aftermath of Emergence Day — the defining event of the Gears of War universe — for the very first time and tests your mettle in highly competitive new multiplayer modes. 

Set years before the events of the previous Gears of War trilogy, Judgment centers on Kilo Squad, a troop of soldiers led by Damon Baird and Augustus “The Cole Train” Cole. They are joined by newcomers to the Gears series, Sofia Hendricks and Garron Paduk, as they attempt to save the besieged city of Halvo Bay from a terrifying new enemy.  Gears of War: Judgment depicts the planet Sera on the brink of annihilation by an unstoppable new Locust menace, giving you a new vantage point into one of the richest and most acclaimed sagas in gaming.

As with all Gears of War games, Judgment delivers intense co-op gameplay.  Play cooperatively with up to three friends on Xbox LIVE (four players total) and experience more challenging gameplay scenarios and achievements by uncovering critical information during the course of the campaign with Judgement’s all new “Mission Declassification” system.

Gears of War: Judgment also introduces a new Smart Spawn System [S3] for both campaign and multiplayer action. This new system ensures that each encounter is unique and new because types, timing and locations of enemies change with each new encounter.

Finally, Gears of War: Judgment introduces Gears players to brand-new multiplayer experiences like OverRun, a thrilling new class-based competitive mode that pits Locust and COG soldiers in a head-to-head battle unlike anything Gears fans have experienced yet.  OverRun is an objective-oriented mode that lets five-player teams alternate between playing as Locusts and COG soldiers, and marks the first time that a class-based, competitive multiplayer experience has been introduced in the Gears of War series, amping up the addictive gameplay with a deep player progression system layered on top of the experience.

Additional game modes will be announced at a later time.

The final part of the announcement, which mentions a release date is towards the end of the article

Gears of War: Judgment will launch worldwide in early 2013 and will be available exclusively on the Xbox 360.