This piece says it better than I can. Rubicon is really two shows, each one has its own plot, mise en scène, themes. It practically had two different creators. And the stuff from the 1970s just isn't as interesting as the stuff post-9/11. What was most disappointing is that the season ended on a flourish influenced by the former rather than the latter. Truxton Spangler's motive is some conspiracy beyond even his control, rather than the much more chilling revelation in the fourth episode, where he switches off a call from his nagging daughter, and tells Will about the "gift" of distance. Intelligence, government as a whole, is about seeing people as patterns and numbers, not as people. This is all Spangler knows (I wonder if the name is a reference to Spengler?) There is no empathy there. Just the joy of seeing the connections, manipulating the actors, executing the most daring and audacious plans, and impressing his cabal of school-friends.
Pace-wise, Rubicon has its moments, but it can sometimes be a slog. The nonsensical plot and the absurd institution at the centre of the show (where everything is on paper, and everyone has too much time on their hands) doesn't help your investment in the story. The opportunities for extremely rewarding character work were not taken. Instead, Grant starts off an asshole and inexplicably morphs into dependable rock. His infidelity, Tanya's substance abuse, and Miles's failed marriage get perfunctory treatment. They are little asides to add a couple of extra dimensions, before we get back to Will's quest for answers. I would have preferred it if the show abandoned the season-wide narrative, and instead did standalone episodes testing the characters' personal, ethical and political mindsets -- like the episode midway through where the team have to decide on whether to order an air strike in an area full of civilians, or when Tanya and Miles witness U.S. sanctioned torture.
...but if I wanted that, I might as well have just gone and re-watched my West Wing DVDs, right?