A truly successful epic novel*, one that covers very long periods of time, is a tricky undertaking. You have to provide enough information to feed the appetites of history buffs, but you also have to balance that with a convincing human story. Rutherfurd doesn't quite achieve that balance.
Long time spans in a novel require a circus truckload of diverse characters. And at least a third of those characters have to be rich and interesting rather than an endless line-up of Whats-His-Name, So-and-So, Bad Guy, Good Girl, That-Weird-Dude-Again, etc. Rutherfurd's characters are more of the latter, unfortunately. There are a couple of stand-outs but the author gave each generation of the novel's core families repetitive traits (stuff like unusually long toes, short stature, criminality, etc.)causing them to blur together. I got a bit tired of each family replaying varied iterations of its genetic destiny. (The short guy always gets the short stick. Every. Single. Time. That one family is always nefarious. Always.)
The characters become less wooden outside of their personal dramas, when they're responding to larger patterns of political intrigue, plagues, changing technologies, and war over the centuries. That's where this book is at its best. The coming of the Black Death and the construction of Salisbury Cathedral were both particularly interesting.
So, to sum up: the historical part of this book gets an 8 out of 10, the novel part gets a 6.
* Truly successful epic novel usually = James Michener