I'd been curious for years to see this thing, both because of the very interesting actors, and the period setting. Now I've just watched the British DVD, and found that its absolutely brilliantly done, and compulsively watchable. Its basically the saga of an "extended family" from 1939 to 1984, focusing on the females - all of them quite lively, and several of whom have luckily married into money. The characters are admittedly somewhat shallow and self-centered, but nevertheless fascinating. The acting and direction are so wonderful, and the story is so intriguing and amusing, that it all just flies by, leaving you wanting more. I suspect that this is one of those rare times when the "film-version" improves on the original book. Kudos to Channel 4 for having successfully tackled another edgy piece of material.
It takes some time getting accustomed to the affected and presumably somewhat archaic upper-middle-class accents assumed by some of the actors. The occasionally plummy and arch dialog, particularly between Calypso and Oliver, started to remind me strongly of watching Rex Harrison and his wives elegantly sniping at each other in "Blithe Spirit (1945)". As an American this blows right by me; I can only guess that, for the UK audience, the accents will place the characters very firmly in time, place, and class.
Trivia note: young Sophy is played by Rebecca Hall, who is the daughter of the director Peter Hall. She turns in an amazing performance.