Things wrong in this episode. (I probably won't remember half of them.)
Abysmal battle tactics. Dohrakki charge in darkness into their deaths instead of waiting. Cavalry is best used for flanking manouvers. Trebuches should be behind the troops. When you know from where the enemy attacks, you set up ditches, traps etc. Why were the unsullied infront the first line of defense? When you know the enemy likes the night and hates fire, why not set up many fires for light? Bad use of dragons. etc...
Melisandre. She should have died when lighting the ditch. Everything after that was pretty much meaningless. Bad writing. Arya should have taken the decision herself to kill the NightKing, not be reminded by Melisandre that "Hey, according to my dream you should now go and kill the NK, okay?". Very bad writing.
Various characters got stormed by wights multiple times without them dying. Why?
Old corpses have the power to hit through their stone coffins.
What did Bran do exactly? Nothing by the looks of it.
Arya can teleport. First time from underneath the table, second time to the back of the NightKning. It also appears she can jump unnaturally high.
So wights can hear Arya's blood dripping from half a foot, but can't hear her sneak around, sliding under the table, killing another wight etc...
Why didn't Bran get swarmed by wights? Sure, maybe the Night King wanted him alive, but why keep such a distance?
Theon's death. It would have been far better if he stood his ground and waited for the Night King to approach instead of doing his suicide run into the group of white walkers.
The Night King smirking and taking no damage from dragonfire. This was made up on the spot as DB Weiss stated ""We thought it was important that whatever the plan was it doesn't just work[roasting NK with dragon fire] because that would be dull." And this is how Dumb&Dumber make their show. It wouldn't be cool. Zombie polar bears anyone? /sarc
You know what would have been a lot better? Making the Night King smart enough to not get into a situation where he could potentially get harmed. He has other white walkers that can do his work for him. And speaking of them, where were they?The Night King marching into Winterfell. As I understood correctly, he can see through the eyes of every wight. And moments before he chose not to fight Jon Snow (he could have just killed him with all the wights around helping). So why does he risk going into the castle when there are still lots of people alive and dragon glass laying around everywhere?
Dany lets her dragon get overwhelmed by wights which ultimately led to her falling off. Just fly off or burn the ground.
Ofc Dany doesn't have to fear the wights as Dumb&Dumber have given her the magical plot armor in the form of Jorah, who somehow always knows when and where he needs to be. And quite conveniently, he survives just long enough to keep Dany safe until NK is killed. Fan-fucking-tastic.
As stated by someone else. The Night King had all the means to simply surround the castle and wait until they all froze inside. A little patience goes a long way. This again is bad writing. If you need your enemy to attack... he needs a reason. This would have been a wonderful time to use Bran somehow.
etc... I'm tired.