It's a good read. The way it's presented as an historical account gathered from multiple sources, some of which cannot entirely be relied upon, makes for a unique storytelling technique. Sometimes it's sort of like reading a tabloid account of a historical event, while at other times, it's a fairly straightforward accounting of what happened.
The good thing is that even if you read it, the details of the book are vague enough that there's plenty of room for artistic license when it comes to how they're portrayed in the show, so while you may know where the story will ultimately go, you can't be entirely sure of how they're going to get there, so there's still some mystery to watching the show.