'Artistic License' and Possible Spoiler
I know I'm gonna get some heat about this, especially since I've yet to see it. However, I have read all three Musketeers books. Yes, there are three of them, they are "The Three Musketeers", "Twenty Years After", and "The Man in the Iron Mask". Here comes the spoiler: At the end of "The Man in the Iron Mask", D'Artagnan is about to receive his commission as Field Marshal. Just as he opens the case containing his riding crop, he gets a cannonball right in the chest.
I mention this only because from the descriptions I've read, they have D'Artagnan retired and living in the country. Now while that's what we'd all probably like for him to have done, it didn't happen that way in the books.
Yeah, I know, I'm probably being petty about it, and that's why this post is labeled "Artistic License". It's what happens whenever they "adapt", or make a film "based on the works of...".