Dark Sector multiplayer features detailed
Here. Dark Sector's multiplayer is broken up into two distinct game types, Infection and Epidemic. In the former, one payer takes on the role of protaganist Hayden, the others as up to nine bad guys. In the latter, players are divided into two equal teams.
Read more through the link. D3's sci-fi action slasher's out at the end of March for 360 and PS3.