I think I can compare watching this show with a comedy with a 'laugh-tape' underneath. I don't need to hear the laughter to get that there's a joke, but I won't laugh at the joke if the joke isn't funny. With "The Americans" I can see it, but not 'feel' it.
Maybe that a lot of that feeling is due to Elizabeth. This is by no means some dig at Keri's acting. I think she's doing a good job, I get where Elizabeth is coming from, I can understand her worries for her kids etc, but I don't give a sh**. If she is concerned/worried/scared about something, I just end up rolling my eyes and think 'get over yourself, drama-queen'. I think it's because Elizabeth has been an ice-berg for too long, that her about-turn just feels incredibly fake to me. I'm more concerned/have more compassion for Sandra, Nina or Martha.
Maybe it's knowing that Philip/Elizabeth will always get out of it alive, is what takes the sting out of these episodes as well. Like watching an episode of the A-team, you just know that, regardless how well the trap, they will get out of it. No worries. (Unfortunately the 'ways out' for P/E aren't half as entertaining as the A-team's. :S)
I think that Matthew is doing an phenomenal job in showing off his acting talents, he makes each character a different one and I watch in awe of his subtlety, the nuances on his face, the way that he uses his body and everything, but I'm not engaged in Philip at all. Again, there's no need to be worried about him either.
If Matthew hadn't been in it, I would stop watching this show. And though I know that Matthew likes this role, because he does get to slip in all these different disguises and I want him to be happy and with a steady job and such, a part of me wouldn't shed a tear if this show got cancelled tomorrow.