The Hero's Path

Although the idea of "cooperative gameplay" (if not "competing") is easier to implement in something like Warcraft than in Heroes, and the main quests are very different in difficulty for such a thing (although you can simply divide the functions - someone provides food, someone provides horses, someone robs caravans). + potions/artifacts cannot be transferred between players.

In any case, this makes sense only if you are interested in implementing something like this, but if it's just a formal "they complained that," then it's not necessary, sorry for bothering you with this.