There are going to be some spoilers for parts of the season, but I’m going to avoid specifics of the finale itself. You have been warned.
From the very first episode, the way that Nate has been portrayed in season two is at odds with the way his character was established. He was full of himself and rude to people in episode one, and then he got so froggy he kissed Keely (seriously, does everyone on this show want that woman?), and then of course the big story from the final two episodes.
By the beginning of the finale, Nate somehow has developed gray hair, which I don’t remember being a thing in the rest of the season at all. This is just the most obvious visual example of my perception of his character development – none of it feels earned. There’s nothing in the season that serves to truly explain why he’s gone from being a loving team member to a raging narcissist.
Bill Lawrence has said that the show was meant to have a three-season arc, so that final season is going to be a challenge to write and make us feel good again.