I'm finishing the Darth Plagueis audiobook. It is ranked on many lists as the best Star Wars book.
It is very much a prequel to the Star Wars Prequel Trilogy. I think that it ends shortly before Episode 1 begins. What is interesting is how it shows all the events that lead up to Episode 1. There might be too much politics for some people, but Plagueis is shown to be the behind-the-scenes mastermind who engineered the fall of The Republic.
Palpatine gets equal time as he progresses from a young apprentice to a Sith Lord. His interactions with Plagueis are interesting.