West Side Story is terrible. Of course many critics like it, because (in my opinion) they think it "highbrow". It's an adaptation of Romeo and Juliet, and the music is by a classical composer, Leonard Bernstein. Nonetheless, the score is sappy mush (can anyone listen to "I Feel Pretty" without being nauseated). The cast is terrible - neither of the leads can act or sing. And the script is ridiculous. When one's mind's ear hears, "Oh, I am fortune's fool", the movie's hero shouts, "Maria!" over and over.
A few of the songs and dance numbers are OK, but in general the movie is not even close to Singin' in the Rain. Complaining about a lack of narrative in a Musical is like complaining about a lack of singing in a tragic drama. It's all about the songs and dances. The light-hearted, jazz oriented numbers in Singin' blow away the balletic schmaltz in West Side. I never saw West Side Story on the stage, and, by reports, the dancing was innovative. In the movie, it doesn't work. It's meant to capture the teen angst of disaffected youth -- but the gang members look more like ballerinas than dissaffected youths. The best number is the one backstage number -- the dance in the gymn.
"Say it loud and there's music playing / Say it soft and it's almost like praying..." Barf!
I'll grant that mine is not a standard opinion (the movie won the Oscar), but it is the opinion of a huge movie-musical fan (me). Nothing in West Side Story comes even close to the "Singin' in the Rain" number or the long "Broadway Melody" ballet at the end (starring the incomparable Cyd Charisse, who also starred in the superb "Band Wagon").

