This is the 1948 version, starring Gene Kelly. It's actually pretty good! The swordfights are a lot of fun, because Gene Kelly adapts his usual athletic style of dancing perfectly. So lovers of swordfights that sometimes have more jumping around on unlikely props than actual swordfighting sould enjoy it.
The problem, and I'm surprised to say this, is that it's too faithful to the book. All the subplots are kept in, and that means there are long stretches of "drama" between the fun. Have you ever read The Princess Bride? You know how William Goldman just kept "the exciting parts" and took out the dull stuff? This movie still has the dull parts. It could be edited down to a tremendously fun hour, though, full of swordfighting and wall-climbing, and derring-do. Gene Kelly's a lot of fun, and it's entirely plausible the way everyone looks at him admiringly. The duel where D'Artagnan meets Athos, Porthos, and Aramis degenerates into the other three watching him and applauding. It totally makes sense that these guys are instant friends.
The supporting characters are exactly as good as they should be in a lavish Technicolor movie like this. Vincent Price is Cardinal Richelieu! Lana Turner is Milady de Winter! Angela Lansbury is Queen Anne! And so on! It's a lot like The Scarlet Pumpernickle, really. And that's good, because it's one of my favorite Daffy Duck cartoons.