Everything about Season 4 was superb to me when first watching it, EXCEPT that exact point! In fact, I thought it was the very first time in all four seasons that GoT had a visible (that I noticed while watching it) plot hole. Everything about the show, every single episode, up to that point, felt like a naturally occurring story. One thing was leading to another with surprising but logical twists and turns.

Then this "betrayal" happened.

It was the first time ever it felt like something happening in the show wasn't a "real-world" (within the show) event - it was immediately immersion breaking. I was watching a character doing what she was doing not because her character development and the plot had led her to do that in her world, but because the writers of the fake TV show I was watching were making her do that on my TV screen, to force a new soap-drama plot point that they had not developed.

I remember looking on Reddit to see what others were saying at the time, and people were proclaiming "yeah, that was supposed to happen, she was like that in the books too!" But after looking into it, it sounded like in the books she never had any scenes where she was doing the right thing or actively trying to help when no one knew what she was doing. She was only pretending to do the right things and help when she thought it would be public to someone(s).

But in the show, there were multiple scenes across multiple seasons where she clearly tried to help and/or do the right thing when it did NOT potentially benefit her and when it would have been more beneficial if she did the opposite. Yet suddenly all at once "yeah she has been pretending from the beginning" - when it was very clear in the show (because we the audience were shown things that only we knew, despite other characters not knowing) she was not pretending in any episode previous to her betrayal.

They literally retconned her character. Was the first time I noticed a bad plot problem in GoT. As I said in another post, I have no confidence in GRRM's ability to give a good conclusion to a long/complex series, but I don't think it is a coincidence he left after the end of season 4 due to "disagreements" with the showrunners. I bet how that plot/character was handled in particular was one of multiple final straws for him.