This was apparently Mark Twain’s favorite of his books. It’s not bad, but I think you have buy into Twain’s level of adoration of Joan in order to really enjoy the book. It’s a weird novel. The great satirist, usually en garde with a rapier’s wit, is totally defenseless in his earnest telling of the story.
It suffers at the beginning because it’s all about Joan, who is constant and immovable as a character. She never doubts, never questions, never shows a hint of cowardice. This makes for a dull start. But as the book progresses, Twain adds characters to her orbit that change and mature because of their association with her. Ironically, as the book focuses more on the side characters, we can see Joan more clearly because of the effect she has on her friends.