At the Game Developers Conference in 2011, Epic Games showed off a new demo of their widely-used Unreal graphics technology. The Unreal Engine drives a ton of popular games, from Gears of War and BioShock to Borderlands and Arkham City. The demo Epic showed was a violent, action-packed piece of work called 'Samaritan," and it impressed the heck out of everyone. You can watch it above.
The demo was using their current engine (believe it or not), the Unreal Engine 3—the Unreal Engine 4 was shown at last year's E3.