[HamiltonJay]

Well, the one thing they still need to address, are the Night Kings intentions, and motivations... at least as far as I know, that has yet to be explained. They don’t need to, but the best villains aren’t just empty canvases...

I would expect some sort of big surprise surrounding that, before this is over....

[LibertarianLiz]

I believe that Bran explained in the last episode that the Night King wants the Long Night to return. It seemed to mean that we would lose what makes us human, our emotions, our memories; and, darkness.

The Night King and his dead army can live in that environment --- humans really can't.