The Richard Lester movies are remarkably true to the book. I love them both.
Alexandre Dumas was well aware of his heroes' flaws, just as Ian Fleming was well aware of James Bond's flaws, or Sergio Leone was well aware of The Man with No Name's flaws. The swashbuckling genre generated by The Three Musketeers was often far less cynical than the original. Lester restored the hilarious cynicism of the original book.
D'Artagnan has several love affairs and tricks Milady into sleeping with him while she thinks she's sleeping with her lover -- and despite the fact that Constance is supposed to be his girl. Richelieu is actually much smarter than the King and has France's welfare in mind. Ultimately, D'Artagnan ends up working for Richelieu and becomes good friends with Rochefort, who appeared to be the big baddie at the beginning of the tale.
It's all a big game, life is cheap, and what redeems our "heroes" is that they are brave, daring, clever, and just plain awesome and the people they kill are either non-entities or truly villainous -- even more villainous than our heroes.
Yes.