The stuff with the baby was heart-wrenching. However, I've come to find Masters and Johnson my least favorite characters on the show, so an episode that consists mostly of them in a hotel room didn't really do much for me.
I really miss the study. Really, really miss it. Season 1 dealt with a bunch of flawed characters, but the study injected some humor and a genuine excitement about science (or at the very least an unsurprisingly genuine excitement about sex) into the show. Season 2 has been all flawed character without any glimmers of the warmth and humor that worked so well to balance things out before.