The best part about it is the stark contrast to everything else usually happening in GoT: The plot is mainly driven by dialogue. Sure there's the occasional action or love scene but first of all dialogue dominates the show. It's verbal confrontations and mind games. Intriguing. Challenging.
All of a sudden and almost half-way into the episode the viewers are cought completely off guard and are confronted with stuff happening left and right and (almost) no dialogue at all. Abruptly the viewer is left all alone, lost in the chaos and dread of the battlefield, with quick shots and camera angle changes, powerful music, the buildup is enormous, finally the wooden wall falls, zombies charge on, people scream and die and the WW eerily watch from above the cliff. People run for their lives, a few brave ones attempt to battle the onslaught. They hold them off. They even try to get a hold of the rescuing Dragonglass. A WW appears and almost defeats our hero. In a last desperate attempt to get out of there alive Jon swings his sword - and kills the WW. What?! But you don't have time to try and comprehend. An avalanche of the dead is let loose. Get out of there! They manage to get the last boat. As they look on the shore and the piles of dead in total silence, the NK steps on the dock. With a taunting 'come at me bro' motion. Oh ****. You think it ends there. But no. It gets even darker and more threatening: All the fallen, the ones we learned to care about, rise up and join the mindless and ruthless army of the dead. No words. No music. Total silence. Just the wind howling. The viewer is left in shock, awe and fear. Just like Jon. Cut! (cue the Lost sound at the end of mind**** episodes)
Perfection.