Spoilers **
I've now watched all four episodes and I think I would have enjoyed it more if I hadn't read the book.
Some of the casting was spot on (Hugh, Teddy, Pamela) but the younger Ursula was too old and the older Ursula was too young, and I don't understand why every incarnation of Ursula was so passive and drippy, with that awful John Lewis music baby-voice.
The whole atmosphere was too sombre and despairing, whereas the book was full of humour and verve and pace.
The Blitz and Berlin sections lacked the epic scale and drama of the book. When Ursula was having the conversation with the Berlin pharmacist I thought we were being told and not shown. In the book you really get the sense that the Red Army is at the door and Ursula doesn't need to give a speech explaining why she does what she does. (IIRC, neither does she explain to Pamela about being raped, which l felt was more about unnecessarily clarifying for the viewer that what happened was rape and rape is wrong. The book trusts that the reader understands the howling injustice of the situation. In fact, Ursula having to carry a 'secret shame' is part of the whole unfairness.)
My main moan is that too much was missed out: Izzie's secret baby who was raised in Germany; the Shawcross family and Teddy's childhood sweetheart, Nancy, who was murdered/alive depending on the timeline; Ursula befriending Eva Braun and becoming close to Hitler's inner circle; most of Ursula's rescue work, relationships and friendships during the Blitz; all the dogs. What was there was mostly beautifully done but the whole thing was stripped of flavour.