I agree with everyting with what you guys said, but, still, i enjoyed this episode a great deal, even with the anticlimatic ending. Actually it was more satisfying for me than Avengers Endgame.
The battles scenes were great, the dragon fights were awesome, the music was really good and i was in a state of tension throughout the whole episode, something that few movies or episodes achieved so far.
Now to the minuses, as you all pointed out i think an important character should've died, Arya for example, at the last scene, they could've made her sacrifice while Bran would kill the NK with some of his magical powers, or something.
Also, they could've killed Danaerys just because it's Game of Thrones and they put her in a position she shouldn't have survived.
Why the hell is Ghost still around and is shown at the beginning of the episode and after that you can't see him anywhere, he is not seen getting killed, he is not seen chewing on an undead bone, he vanishes, and this happened throughout the last 3-4 seasons. It's really weird.
About the Night King's death, they should have done it better, way better, but i'm still hoping they are going to introduce something that will tell us that he is not dead, just dormant for a while, or something. Or maybe Bran will transform into the Night King, or just like the three eyed ravens trained a new three eyed raven, maybe the same happened with the Night King, too. The reason why i think it's improbable that the Night King story has ended here, is because, from what i understood from the seriese and the books is that when he is gone the winter will be gone as well, but i might remember it wrong.
Now, about Night King's motivations and why he wants to kill everyone: i think you can figure that out from the series and books, since they talked about this.
The Night King was created by the children of the forrest, when they were at war with the men that invaded the island of westeros 10k years ago, to kill men, so that's what he is doing, he is doing what he was created for, something like a robot that was set to kill all and he won't stop until he does. And i'm fine with this explanation, he is someone you can't negotiate, you can't blackmail, you can't reason with, he's reason of being is to kill all men.
But, this thing makes his "easy" killing even less logical.
In the end, again, even with all the writing problems of the episode, i still enjoyed it sooo much.
And a last thing about the writing, it's gone south after they surpassed the books, and probably that's why GRRM is taking sooo long to write the next book, he is trying to avoid an easy solution like they often chose in the series.