Having powered through nearly 2 season recently I find this show incredibly uneven. Everything between Claire Danes and Damian Lewis is amazing. Mandy Patinkin is a force, though he's basically Jason Gideon just a bit more slick. David Marciano and Maury Sterling just work so well. They are the perfect mixture of comic relief, sincerity and cloak and daggers. Rupert Friend's character is also pretty fun to watch.
However, everyone else just seem uneven. Ironically Morena Baccarin's character come off a bit manic and is there because everyone needs a love triangle (square). David Harewood bounces between moron, douche, hard nose, competent depending on what the show needs. Morgan Saylor is even worse. Her character is basically just there to drive the plot in one direction or another. Diego Klattenhoff's character is there for the same reason, but he pulls it off better. The other characters are kind of just there. I mean I literally forgot Jackson Pace was in the show for a bit.
Still, the show isn't bad. I like how it's more cloaks and less daggers. But thankfully the cast is good, because honestly, if the acting was bad this show probably would not be as popular as it is.