The Undying is not fun.
Rohan has an excellent post about this achievement. In it he, he says everything I’d love to say right now but can’t — because after shaking like a leaf for the last three hours because I was completely and utterly terrified that I would be the one to ruin it for my Naxx-10 group, and then losing our fury warrior to a some bizarre combination of server lag and an iceblock in the last six seconds of Kel’thuzad’s (un)life …
I have no words of my own. None. At all.
This achievement is. not. fun. It is nerve-wracking and guilt-producing and every bit as much about luck and lag and RNG as it is skill and control. I don’t care how close we were; I never want to attempt it again.