Originally Posted by DoctorWho

I'm going to assume that four players on Heroic is going to be too easy since it was already suggested that Normal has been watered down this time around and Heroic is best for single player.

Four on heroic is fun, but not hard. Four on Legendary is hard but fun and eminently doable. There are more things to reveal that will make co-op on Legendary double-Legendary.