"The Siege is a brand-new style of gameplay embracing the reality of counter-terrorist operatives across the world: intense and asymmetrical close-quarters combat between attackers and defenders. In this trailer, a team of gamers select CTU Operators and coordinate their plan of attack in a 5v5, PVP multiplayer battle to secure the objective.
Defenders have the means to transform their environments into strongholds; they can trap, fortify, and create defensive systems to prevent breach by the attackers. To face this challenge, attackers now have a level of freedom unrivaled by any previous Rainbow Six game. Combining tactical maps, observation drones, and a new rappel system, they have more options than ever before to plan, attack, and defuse these situations." -via Ubisoft
Beta will be open on September 24, 2015.
Here is the newest trailer: