My love for Dumas's novel first came not from the book but from the adaption presented in 1993 with Kiefer Sutherland (huge fan). The 'Three Musketeers' movie was one of my favorite movies for quite some time.
So when I chose Dumas's real version of the "Three Musketeers" I at first had a hard time matching my image of the main characters to those in the movie. Parts of their back stories fit but much of their personalities where way off.
Also the story of Milady completely differs in the book than in the movie. In the movie you start to feel for her and Athos. You want her to change her ways and those to win out in a 'love conquers all' way. But in the book you really hate her or at least I did.
And where in the movie the main guys antics are funny and over the top, the book was mostly just over the top. Though I do wish they would have been able to make the scene from the book where they are in the fort having a picnic to win a bet and talk privately into the movie. It was one of my favorite parts of the book that was skipped in the movie.
Though if I was going to mention parts that the movie skipped I would be writing till next week. The movie really seemed to derive it's own story line.
In the end I would still recommend the movie to someone who wanted a good swashbuckling adventure.