If you think this has a conventional hero's journey story arc, you haven't been paying attention.
-Ramsay Snow
It's like a whole lot of people thought it still had one, only that the *real* protagonist was someone else than the apparent one, or rather, who all the other dumb plebs thought was the protagonist.
I thought it was a decent ending. The world has been saved at great cost, all the great houses contending for the Iron Throne have all but perished and exhausted their power. The final assembly of the "great houses of Westeros" has its share of personalities who previously were nobodies but now have filled up the power vacuum, which made it all the more case in point. They don't want any more of the game of thrones, so they choose as king someone who isn't quite human but wise and beyond the ambitions and follies that led to the game of thrones in the first place. That, and lacks the independent power base to bring the great houses to heel in case of conflict, which suits them eminently well.
Sure, a great many viewers expected Jon to be chosen by the assembled lords, and to end the series sitting on the Iron Throne wearing his usual emoface. Jon, who just recently had killed Daenerys knowing fully well that doing so will probably lead to him dying horribly. He sacrificed himself, and his plot armour was only thick enough to mitigate it to exile and banishment.
The descent of Daenerys into madness, though? BLECH. Sure, the elements were there, but there are so many better ways that whole thing could have happened that would have led to the same conclusion. The way it happened was utterly random and almost out of the blue. She had effectively won the battle, her enemies were either surrendered or dead. But let's still have her lose her shit and start laying waste to the city, because Frick if you rooted for her as the liberating hero.