Return of Reckoning

If you think that's bad, I guess you didn't play Guild Wars. Where mobs would do fun stuff like several mob rdps all bursting same player from stealth, or say caster mobs actually chain aoe on party, while mob tanks make sure your party can't get to casters.

Would take something like mob SWs being able to stealth, and starting the fight by 3-4 of them hitting the same party member with Festering, to relive the experience.