I played Age of Conan and was doing the Tier 4 raids, something not many people were able to because Funcom made such hard encounters so I kind of expected hard content, but my god the Nightmares are pretty damn difficult for 5 man content. Lots of different skill and passive synergies for the whole group. Alot of stuff going on and a ton of damage flying around. Its seriously rewarding though to clear a dungeon and I've only done Polaris so far and we cleared it but it was definitly unexpectedly hard for 5 man content.
ProbablyGettingNerfed - L100 - Witch - Path of Exile