Resistance 2 Coop question

I just got Resistance 2 for christmas this morning, just loaded it. My brother and I wanted to do co-op, but single player campaign appears to be just what its name entails, one person. So i wondered can we play the online co-op before beating the single palyer campaign. Whats the online co-op about. Whats the offline co-op about, it show levels, but it starts in chicago and appears to have no story.

I really liked Resiistance fall of man and am still confused and maybe a littel vexed isomniac decided to have the bright idea of having a sole single player campaign after the last resistance game allowed for co-op.

sorry bump, hope I don't get locked.

I really want this answer, my brother and i figure we'll go online, but do we need to do single player campaign first?

Also not to be rude, but can anyone explain why insomniac cut out co-op for campaign and is four player free for all possible offline?,

R2 is a great game, but insomniac really screwed up a few things this time.