Thanks for the replies.
I understand that in the first game everyone "makes progress" as a party and there is story progression. However, the 2nd player is simply "possessing" one of the team members of the host's team. As soon as the game session ends, the 2nd player basically has nothing.
Now the difference (and what I'm trying to figure out), is like in other multiplayer games (ARPGs like Diablo, or MMOs like WOW), where everyone has his / her own characters and progress towards the overall campaign, but can join others and complete quests / campaign.
My friend doesn't think he'll enjoy turn -based combat, so the only way he would get into this, is if we co-op, but he wants to know that his own characters are progressing (so he isn't interested in just playing Robin to my Batman (in a Batman game)...not sure if that makes sense...