Speaking from a 10 man point of view I think heroic Zon Ozz and Warmaster were up there in difficulty. It took us over 100 attempts to get Zon Ozz (we were working it pre nerf) and 1 shot it the day the 5% came out. We were so close with sub 1% wipes before that. Spreading out your 10 man team to deal with the adds properly was very tough and needed to be very comp specific, it was hard to justify more than 2 melee on that fight.
With Warmaster our brick wall was simply the fire bug. Took us over 100 attempts as well. I mean jebus could we fix a fight while its relevant? There was no way you could chance standing in fake fire that was not really there on 10 man and risk a death. Using a BR before Ph2 was just out of the question.
I agree about the rest being kind of lacking from a heroic mode point of view. Were working Spine now and we definitely see the point about approaching it in different ways. We actually have enjoyed working that encounter more than any other so far because it allows us to work as a team and explore new options. Its refreshing.
There is something so appealing about backhanding someone across the face with a shield.