BioShock 2 multiplayer you all wanted so very much after the first game. You'll play as a Plasmid test subject working for Sinclair Solutions during the fall of Rapture as you battle other players in re-worked game locales like Kashmir Restaurant and Mercury Suites.
Victory over your opponents will yield experience that you can spend on new Plasmids, weapons and tonics. If you can take it, you can read all about the mode right here. The mode's being developed by Digital Extremes, which you likely remember for its work on Dark Sector.
... Hey, why do you all look so depressed? What? Us? No, we're not crying. Why would you *sniff* think that?