I agree with 2D beat 'em ups I used to love Double Dragon and Final Fight!
Another thing I'd like to see come back is a score mechanic. A lot of the replay value in the old games were from improving at the game and achieving a new high score. Trying to get a new high score gave you urge to play it over and over again. A lot of the single player campaigns most people want to run through them and once they're finished they don't have the urge to come back to it again. I think with an arcade/score mechanic would be great in creating more replay value in single player campaigns. Somethin like Housemarque does with their games have a multiplier that builds up and it goes down when you take damage.







