Let's start with the obvious, this film is incredibly stupid.
It's story is all over the place, it's overly ridiculous at points, the film can't decide which character it wants to be the villain, some of the CGI is pretty terrible and its editing is laughably bad.
But in all of its stupidness I kind of enjoyed it. I enjoyed the characters and performances and found alot of the action set pieces and fight scenes (particularly the ending fight between Lerman and Mikkelsen) to be pretty entertaining.
The Three Musketeers is overall a very stupid movie but there's alot of fun to be found in its stupidness.