Do you think the beats of the plot would have worked as an ending still? Wight's get owned, Cersei gets owned, Dany goes mad, Jon kills her? I feel like half a season of Danerys as an evil ruler would have been fun.
To me watching a show the most important part of enjoying it is seeing the characters develop properly. I would have had no problems with some of the above provided we had seen some examples of those characters actually going mad. But seeing nothing, makes it really hard to accept. You then have characters just reacting to situations rather than understanding why they act the way they do. I think that approach also helps the actors too, as there is some substance to how they react as well.
I am watching His Dark Materials at the moment on BBC1. All of series two has been taken up developing the two young characters and you can't believe how much better it makes a show, say nothing of enabling the actors to show how that relationship is going. All the emotional moments are better because you can understand how its come about, as you've seen it yourself on the actual screen. GOT used to do that especially in the early days, but it started to lose its way after the books dried up.
I can entirely understand that my enjoyment may not be the same as someone else's. But I just feel like the show was more interested in these big events, then actually taking the characters themselves any further forward.