Officially set in the summer of "sixteen hundred and something or other", this is an unapologetically anachronistic crossover of two proven swashbuckling staples. The Four Musketeers are little more than the backdrop for our dashing protagonist Zorro, but that's totally in character for them, given how the original Three Musketeers are often portrayed in the same relationship to d'Artagnan, their number four.
The setting is the court of King Philipp II of Spain (1527-1598) and the French-Spanish border during one of the numerous wars between these two countries. Lady Isabella, a cousin of the Spanish king, is held for ransom in France by Cardinal Richelieu (1585-1642), with the reluctant (in fact disgusted) participation of the famous Musketeers. Zorro (usually depicted as a resident of Pueblo de Los Angeles, settled 1781) is incognito at the Spanish court and sets out to France to free her single-handedly, disposing of a treacherous rival on the way. From here the plot unfolds pretty much how you would expect it to, given the characters.
It is doubtful that fighting was really exactly the same in the early 16th century and in the late 18th century, but in films it is almost always depicted in the same way: People usually use their rapiers; guns exist, but they are cumbersome and unreliable muzzle-loaders that almost never hit their targets. This is why Zorro and the Musketeers go so well together. Zorro has a bit more cunning and the Musketeers a bit more fighting prowess, but overall they are quite similar because they all fit the swashbuckling hero stereotype.
I think the same premise could be used for a really great film with deep personalities, where our heroes turn out not to be 100% compatible. Instead, we are getting a rather unsubtle, straightforward pure adventure film. For swashbuckling fans who are intrigued by the crossover, there is no reason not to watch this. But everyone else won't miss much by skipping it.
