although, compared to BRF NH is bland.

1.) The stamp boss, where people got stamped to death. Was hilarious during progression.
2.) Train boss, once again something different (maybe not the add aoe, boss mechanics) but the theme of fighting in the middle of a busy station.
3.) Blackhand-> Hulk smash!! break the dang room.

Heck even HFC had some nice bosses, like socrethar, mannoroth was epic setting (nothing compared to BRF though).

Throne of thunder was golden

1.) Encounter design with having to fly between nests..
2.) A very GOOD council fight
3.) Durumu Maze


It is not so much about the mechanics of the fight itself, but more of the encounter setting. That is what OP is getting at.

like,

Brf Had innovative encounters with trains, ships, blackhand and stampers
ToT had nice innovative settings with Ji kun flying (granted, it was taken of firelands flying), durumu maze
HFC had somewhat with mannoroth (again, not the mechanics) but the encounter settings

Granted Helya felt a little different than the other bosses ( a bit more like sinestra)
and NH guldan has some nice phase transitions.