Kantor on 14 January 2009
"Currently there are no plans for co-op in Killzone 2"
There we go.
No plans =/= not happening. There were "no plans" for a PS3 version of BioShock, remember? Maybe they just want to keep sales in the first few weeks strong, otherwise people would wait for the patch to buy it.
No, I'm pretty sure they'll put in co-op. Even if it's paid DLC.
(Former) Lead Moderator and (Eternal) VGC Detective 
