Golgoroth would always be a brick wall for me. Playing with LFGs the group disbanded quite regularly during his encounter. Everyone seemed to have a different plan for the encounter so people would just end up everywhere and then it'd go wrong and they'd all quit

I hated the Golgoroth part because noob kids would constantly screw it up. It's not that difficult or hard to understand but man did I have some stinkers on my raid teams. I still have yet to complete the Golg challenge mode because people can't follow simple instructions. (Those stupid exploding thrall)