I think this is one of those rare occasions where the "sequel" turned out better than the original. (I use the term sequel loosely, there are a few references to the first book, but most of what happens is independent of that.) Pillars of the Earth was an amazing story, but I think at times it was a little bogged down with the descriptions of medieval masonry. World Without End certainly has architectural elements, but it was usually a couple quick sentences about how Merthin could build something new, but simplistic, that no one had ever seen before. As a result, this book was much more character/plot driven. 
 The same general theme of good vs. evil prevails. There are times when, maddeningly, it seems the only way to get ahead in life is to stomp on all the other people around you, but ultimately, Follett gives the reader the happy ending they were looking for. I was satisfied that many more of the characters received more poetic justice. (view spoiler)[ Ralph killed by his son, Godwyn killed by the very plague he ran to escape, Prior Anthony, though he was certainly not evil, killed by the bridge he didn't want to repair, and Caris's face engraved on an angel watching over the town. (hide spoiler)] This led to a more satisfying read overall, where I remember being frustrated by the way many of the other characters' story lines ended in Pillars of the Earth. 
 I think Follett did an excellent job of trying to portray how people would think and operate in a world that didn't understand how communicable disease was spread (in this case the plague). The muslims believed the disease was transmitted by light beams reflected from the eyes of a sick person. I'm not sure if this is a historically accurate viewpoint, but it was an interesting thought. As was seeing how modern medicine might have found it's beginnings in 14th century Europe. What if the plague had never come? How long might it have taken people to discover why sickness could spread and how? Would we still be bleeding people and speaking of humors? 
 My only real complaint is that there were a few mysteries that were never quite solved. Who was Philemon's secret lover? Was it a man or woman? What happened to old King Edward? And what was the deal with the damn cat! I know he's supposed to symbolize something, and that it could be interpreted differently according to each reader, but I'm curious to know what the author intended the cat to mean. Ultimately, these minor mysteries are of little to no consequence and have no real impact on the story. Overall an excellent book and a must read for anyone who enjoyed Pillars of the Earth.