nope Marcus Fenix, Dom, Cole Train, and Anya did battle with Locust and Lambent Locust, which are powered up versions of enemies that have the ability to mutate during battle. The Lambet Locust emerge through giant tentacles that come out of the ground. The enemies are tough and require precise targeting to remove mutated limbs in succession.
Marcus was also able to take a regular Locust hostage, similar to Gears of War 2, but tagged it with a grenade before kicking it away toward another enemy. Very cool new move.
Epic will also be unveiling a new mode later on at E3 called "Beast", but no additional details were given. Gears of War 3 is an Xbox 360 exclusive and will be released in April 2011.