Guild Wars 2

I would suggest an end game very hard to play for level 80s in the ring of fire taking very large teams to complete a lot of the events, this will get people going and staying there.

Make it be very eventful.

Make it be very hard to take down the event monsters, nearly impossible. This would make for a repeatable end game pve scenario.

I would also maybe put in a person controlled npc that the admins could purposefully trigger whenever they want and control a huge pve boss for players to try to take down.

Make legendaries drop here.

No large teams please, we already have enough of all these zergings.