According to the press release, Killzone 3 picks up right after the events of Killzone 2, with the player having to take on the Helghast alone following the nuclear annihilation of the Helghan capital, Phyruss. The game will include levels “ten times bigger than in Killzone 2,” and will feature a host of varied environments, including “toxic nuclear wastelands,” a “lethal alien jungle,” “bitter arctic conditions” and even space. As Sony puts it, "This is David vs. Goliath…if Goliath had thousands of troops and a thermonuclear arsenal."
Sony also confirmed Stereoscopic 3D support as well as the inclusion of jetpacks, so if those things are important to you, then congratulations. It was already expected that Sony would have something to show off at E3, and this official announcement pretty much seals the deal. Lucky for you, we’ll be on hand to bring you all of the details, so stay tuned.