Guild Wars 2

Instead of making them in a open world where lag, unrendering and other bad things that the huge overflow of players bring. Make them in a instanced area, that work like those quest instances. It would be easier to control, as you can set it be made only once per character and fix most of issues had with this event and the halloween one. It also could be set to be available for a time frame, so every time zone could get a shot on the event.