Don't forget the story line with Quinn's wife and child. I think that was in there to show that he is not just a mindless killing puppet, but that he still retains some humanity. That's why I felt his decision not to follow through with the kill was plausible for me (plus, I think he felt for Carrie and didn't think Brody was a threat).
The romance between Brody and Carrie did turn unbelievable this season, which was unfortunate. The final episode cabin scenes felt very unnatural. I half hope it was intentional -- showing how they don't quite work together without being surrounded by intensity and danger.
As for the mole, whoever it is, I can't help but think it will be disappointing because it will almost certainly be either a bit player or someone we've never met. There's no investment there as a viewer (not to mention I felt the whole mole possibility was handled fairly carelessly by the writers).
One thing I initially liked about this show is that they didn't hold their cards for long. Things happened at a much quicker pace than I would have expected (like that confession video being found in the third episode or Nazir already being killed). However, I think this has forced the writers to constantly one-up what they've done and thus forced the show into implausible plot twists and a de-emphasis on character. It would be nice if the third season was a bit more low key, focusing on a wide ranging, character driven mole hunt.
I kind of wish the show would have ended this season or perhaps taken on different characters/storylines in each season, like Damages, so that they don't have to keep trying to make Brody a part of the show.