Its good, but I am having trouble understanding a lot of the motivation behind the actions of the two lead characters. Masters is kind of a d***, actually, and Johnson seems confused by everything. The writers need to pull this together quickly or I will start to lose interest.
Other than the clumsy storytelling, the cast is great, the story is compelling, and the set direction gives an interesting mid-50's view of their world. It is not overtly or gratuitously sexual, although it might make Granny blush (I don't think I'll watch this with Mom and Dad), and there is a surprising amount of humor, most of it from the prostitute hired by Masters for his "research".
So there is a lot of promise here, but delivery is a separate issue, and unless they get the storytelling aspect a little clearer things could go either way.
Also, I think the title is a little too cute of a double-entendre and a little too on the nose; Masters and Johnson would have been a better title.