I'm a fan of author Kim Stanley Robinson, but I'm also the first to admit that he can be verbose. He can spend a ridiculous amount of space writing in accurate detail about something of almost no interest to anyone. But that just means that his subject is incredibly well researched and that he's extremely knowledgable about the subject at hand. And I say all this to let you know that I found almost none of "Galileo's Dream" uninteresting. Long, yes. But not dull.
If you've read or listened to "Abraham Lincoln: Vampire Hunter" (not watched. The movie is a different beast entirely) then you know that it is essentially a Lincoln biography with vampires used to explain events in his life and actions he's taken. "Galileo's Dream" is a similar take on the life of Galileo Galilei. Only, instead of vampires our hero gets periodically transported to the moons of Jupiter around 3500 AD, give or take. So, most of the book is straight biography. But around far flung Jupiter conflicting factions feud about whether to explore the oceans under the ice of Europa. Galileo is brought forward in time to help advise them on the proper course of action, but mostly acts as an observer. Inevitably, he learns of his own fate and endeavors to avoid being burned at the stake.
As so often happens in Robinson's books, the action picks up 100 pages from the end. That's when Galileo's trial finally starts. And somehow he manages to succeed in saving himself. Then he learns of multiple timelines. While he may not have burned, another Galileo did. And how would history have been different if that Pope had been free to embrace Galileo's writings instead of hamstrung by politics? If the Catholic church hadn't martyred Galileo or even took science into itself?
It was a good book and I'm glad I read it, but you must be prepared to read a book that is mostly an unchanged biography of Galileo with a bit of self reflection thrown in for good measure.