You really need to have some knowledge of the Barsetshire Chronicals to follow it fully. That is why I was surprised, and said to Mr.J2, that Julian Fellowes chose it. Having said that, it can stand on its own, but you need to pay close attention.
IMO Fellowes has done a good job. Dr. Thorne is coming through as a real person instead of a sort off narrator, as the novel left me feeling.
Thoroughly enjoyable (but I had a bit of prior knowledge). Please stick with it you doubters. You will end up loving it, I (very-nearly) promise. :)