The Three Musketeers
Spoilers follow, though this book was first published in 1844 so I'm not sure spoilers warnings are necessary.
I didn't expect this book to be so funny. I was expecting an adventure, with light-hearted elements. I remembered from at least one adaptation I'd seen that d'Artagnan first meets each of the musketeers separately, offends each of them, and arranges duels for the next day within an hour or two of each other. That happens in the book, and it's funny. But there is a lot more comedy than just that. Although d'Artagnan, Athos, Porthos, and Aramis are the heroes, Dumas pokes fun at them constantly and at the customs of France 200 years prior to the writing of the book. I laughed out loud many times while reading this.
There's a great sequence where the musketeers need to have a private conversation, and are worried that they'll be spied on if they go anywhere secluded. This is happening during a battle with the forces at La Rochelle. In order to secure a place to chat, and to give a cover story for why they will be there (not conspiring), they make a bet with some other soldiers that they can hold a tower in enemy territory for several hours. They take the tower (just the four of them and one servant) and make their secret plans while defending it. It is quite fun.
The one disappointing element is how the story of Milady de Winter ends. She is a great villain, and I was rooting for her to some extent. She is captured at one point and her escape is another great sequence.
Overall I'm glad to have read this one, and I expect that I'll read the sequel at some point.