The more I think about it the less happy I am about the way Episode 3 ended. And I think I can now articulate why. The way in which the Night King died really undermined a big theme that the show has been trying to get across, a theme that was especially important in Season 7.

Everyone failed

Whatever way you look at it our heroes lost the Battle of Winterfell, the Dothraki charge failed, the Unsullied were overrun, the walls were breached, the women and children were being slaughtered in the crypts, both living dragons were taken out of the battle, Bran did nothing, and the Night King and his followers just walked into the Godswood to claim victory.

All those armies and all those brilliant fighters and all of Bran’s foresight weren’t enough. In the end Arya basically wins the whole war all on her own with a plan she came up with all on her own (after receiving a hint from Melisandre). We have no on-screen indication that the Night King was weakened from his battle against Jon and Dany, nor do we have any indication that the only reason Arya could pull off this move is because of the battle she was just taking part in.

If our heroes had watched Episode 3 ahead of time it seems as though their best plan would legitimately have been to send the Dothraki south, stuff as many people into the crypts as possible (well-armed) and leave the gates of Winterfell wide open with Bran in the Godswood. Then tell Arya to hide in the Godswood (like she presumably did in Episode 3 after her chat with Mel) and ambush the Night King when he arrived to kill Bran. It would have been the exact same outcome, but that thousands of people would still be alive.

And the result is that the show's big theme of humanity working together ‘we all have to put aside our distrust and fight together against the army of the dead’ is completely undermined.

How no-one made a difference

Jon let the wildlings through the wall in part because he recognised they needed to fight together against the dead. Yet the wildlings didn’t make a difference to the outcome.

Sam went to the Citadel and discovered where the dragonglass was. Yet the dragonglass didn’t make a difference to the outcome.

Jon went south to form an alliance with Dany because he thought he needed her help to defeat the Night King. Yet the dragons and dothraki and unsullied didn’t make a difference to the outcome.

Tyrion arranged the wight summit to convince Cersei that the threat was real. Yet Cersei wouldn’t have made a difference to the outcome anyway.

Jamie abandoned Cersei since he felt it was important for him to honour his word, go North and fight for the living. Yet Jamie didn’t make a difference to the outcome.

Theon returned to Winterfell to fight for the Starks and help save the world. Yet Theon didn’t make a difference to the outcome.

Arya was the only one they needed.

In sum

Episode 3 should have ended in a way that left the audience with the impression that this great alliance of the living was necessary to defeat the Night King, and that if even just one of these heroes had not been present then the battle might have been lost and the world doomed.

Instead, they went for a twist to surprise the audience. It wasn't worth it.