From the "first look" preview:
"Though nothing revolutionary, Marvel vs. Capcom 2 is a title that a lot of players certainly haven't forgotten. Originally released on the Dreamcast in June of 2000, Marvel vs. Capcom 2 was the much anticipated sequel to the incredibly innovative Marvel vs. Capcom. It wasn't just the fact that we now had Mega Man facing off against Spiderman or Ryu taking on War Machine. Marvel vs. Capcom introduced a lot of new elements that the fighting game genre hadn't seen before. One in particular was the tag team system, which allowed a player to trade between characters during combat."