This game is up there and on par with Guilty Gear (imo the greatest arcade fighter of all time). I owned MvC for the Dreamcast and then MvC2 for Dreamcast and XBox (apparently, there weren't many copies of MvC2 ever made, so they're extremely rare). MvC2 got rid of the Crossover Specials (where both teammates fight at the same time), but the expansion of the character list was overwhelming. Always loved fighting as Juggernaut, Hulk and Blackheart against Roll, Servbot and B.B. Hood. Classic.
My fave characters were Strider Hiryu, Gambit and Dan Hibiki.
I've hear they're re-releasing MvC2 onto PSN and XBox Live. When it comes out, I know I'll be counting my wasted time in weeks.