BCTA is a smart, well-written, subtle, and at the same time, emotionally engaging satire of the 60's generation.
It begins with something perfectly symbolic of its theme: an Encounter Session (though you might want to fast-forward through the annoying 2-to-3 minute sequence of a car barreling up the Southern Cal hills to the strains of a truly obnoxious version of Handel's "Halleluiah Chorus" that precedes it; it's the film's only weak point). At this hilltop therapy facility, Bob and Carol are getting to know themselves and each other, on a very deep level, through total honesty. Part of the greatness of this movie is demonstrated in the way this scene is shot: it looks a bit like Cinema Verite, but it is in fact largely scripted film-making(with a bit of improv). It's funny, and at the same time, a little touching. The whole movie is like that.
Carol is utterly converted to what she learns in therapy, and begins spreading the word to others, including friends Ted and Alice. A lot of the movie's humor is generated by the fact that Ted and Alice, while young and trying to be "with it", are really, at heart, a little uptight. And their relationship, as one very funny, and, at the same time, tense sequence demonstrates, is just a bit strained.
The new spirit of total honesty that the characters embrace eventually leads them to some very surprising places.
This is a style of gentle satire one doesn't see currently, except maybe in documentaries. It allows you to laugh at the characters' foibles and care about them at the same time.