I most definitely agree that I would like to see Jamie play more bad guys or at least guys who are less good. He definitely showed he could pull it off with Martin and, putting aside my issues with Joss in regards to Dollhouse overall, I was glad Joss gave Jamie the opportunity to show another side of himself as an actor.
I do feel Martin believed he loved Roma/Echo, but if he truly loved her, even with the betrayal, he would not have slammed her head against the desk. Though points to Jamie for not having Martin come off as a one dimensional abusive husband in the scene. I could definitely see Martin's pain even as I wanted to see his ass kicked for what he just did to Echo.