I am so glad there is a thread on this, I'd hate to think Rutherford's series were not popular. I actually read the Forest first and then read Sarum, and I must say of the two the Forest was by far my favorite. At times, especially the stories around the reign of Elizabeth I and the civil war I was brought to tears. Sarum was incredible but you could tell how far Rutherford had come as a writer between the two.
I havn't read his others, but I'm interested in reading Russka next, seems fascinating.
I wondered all the way through what it might be like adapted into a miniseries, with each episode being one of the stories, all the same actors playing their respective descendants roles.