Nvidia's CES press conference featured a few people playing Shadowgun together, which was a little puzzling, because currently that's impossible. It turns out they were showing off a new version: Shadowgun: Deadzone. The cool new thing about Deadzone, if you haven't guessed by now, is multiplayer support.
Deadzone is bringing all kinds of bells and whistles to the Shadowgun series. It supports 8 player online multiplayer, gamepads, and voice chat.