While last night wasn't the worst of this season, it was still pretty bad in my opinion. I think they only episode I would consider good from this season was episode two, and most of what that episode built up wasn't falled through on.
Anyway, some issues from last night:
1. Jon's decision itself seemed odd. Up until right before he stabs Dany, he was arguing that he owed her her loyalty. His portrayal wasn't necessarily as conflicted, it was "I don't like it, but she's the queen". In the span of minutes, he decides to commit regicide. It just fits with the theme of characters having sudden changes of heart this season.
2. Same thing with Dany. She's mad, remember? Paranoid, blood-thirsty. She just gave a speech getting her army fired up for more war. And, at this point, she's got two potential enemies: the Starks, and Jon, her rival to the throne. So what's she do? She meets with Jon without any guards, and starts making out with him after he just expresses his horror at the dead kids she burnt to death. Dany had been suspicious of Jon previously, and since then, her two closest advisors betrayed her. But all of Dany's paranoia goes away because... the plot needed it to?
3. All of the build up about Jon's true identity don't matter at all. In the end, Dany trusted him despite being a rival. Afterward, nobody acknowledges -- or even brings up -- his rightful claim to the throne. Nobody proposes him as the potential king. Nobody labels Dany an usurper, and tries to make the case that Jon was justified. And, he doesn't get to decide his own fate (even if it's a fate he was probably okay with).
4. The politics of it all are silly. The North declares itself independent. Nobody even raises an argument. Sansa has committed treason / open rebellion, and it's all good. Meanwhile, Yara Greyjoy -- an ally of Dany's -- happily remains quiet, despite the Iron Islands also having a fierce independent streak? She's just good with the plan? That entire scene was weird, being used partially as comic relief (I think?) And Greyworm threatens the use of his army if justice isn't done. That justice is Tyrion and Jon both living, and Jon's brother becoming King while Tyrion becomes hand? Huh?
5. Bran goes from weirdo who can't speak in non-cryptic sentences to a fairly normal guy in a wheelchair? And he all of a sudden is cool with the 3-eyed Raven leading human affairs? As a maker of history, rather than an observer? And all the other Lords are okay with this, without even thinking about it? The guy has no resume at all, other than being the last male Stark. Every time he could have helped, he was completely useless. In one of the final scenes, he suggests that he may be able to warg into the missing dragon. Really? That may have been a helpful skill in the Battle of Winterfell, or in preventing the genocide of King's Landing. But nope.
In the end, eight years of the show ended up essentially meaningless. Most shows do, but GOT was grander than that for a long time.