Directed by Vincente Minnelli, produced by Arthur Freed, songs by Cole Porter, starring Judy Garland and Gene Kelly at the peak of their careers, and shot in glorious Technicolor(*) "The Pirate" had everything to go in its favour. Instead, it flopped. I watched this last around fifteen years ago, and had good memories of it, but watching it again tonight, I can see why. It tries a lot of things and fails at most of them. I think it is an honourable failure.
The music is another problem. This is not vintage Cole Porter: for MGM he did better in "High Society" and even "Les Girls". Even the best song, "Be a Clown" is not at the same level of "Night and Day", "Let's do it, let's fall in Love" or "You're the Top". MGM was probably aware of this, as we hear it twice, in full, within minutes of each other. Also, most of the song and dance numbers drag - particularly "Nina" which adds very little to the plot.
The script is also weak, with not much of a first act, blossoming in the second and then dragging again in the third; and Minnelli probably got tired of arguing with his wife on set (the shooting was very problematic) and lost some enthusiasm. Although it could be simply that having seen most of his melodramas, I have outgrown his musicals, with the exception of the best cross between the two genres, "Meet me in St Louis".
(*) Unfortunately, either because of costs or available materials, the film was not selected by WB to be restored using their Ultra-Resolution process designed for three-strip Technicolor films. Instead something else was used for the DVD. This is a pity, as I think it would benefit the film tremendously if Minnelli's reds could pop to us.