I spent a good amount of time playing the coop this past weekend (as much time as I could break away and control my shared tv, that is). I have exclusively played as the Soldier, because I wanted to see how the level progression worked with just one character, and it was the first round robin default class assigned to me at the time.
When the game comes out, I plan to start as a medic then go Spec ops before returning to the Soldier. From what I have seen on the frontlines, I would rather push the newbies into being the bullet sponges, while playing the school marm and giving orders with healing in the hopes I can foster teamwork out of the box on day one. Thus enriching the online environs the best I can if I can affect it at all.
It kind of sucks, because I want to delve into the other classes, but I want to let that experience be fresh when the game drops.
When you get a group of people together that have a clue or at least a headset, the teams naturally form into the most efficient ratio of class outfits and people don't always have to be the bullet thrower. Maybe it is the beta community, those rabid Resistance fans who are skewing my view of online play, but it has been rewarding thus far and I cannot wait to see the finalized code in the release.