It was terrible. I kept moving on my seat in physical discomfort at the movie's crudeness. I should confess that I'm rather uninspired by dance, and thus was indifferent to the numerous dance scenes the movies is known for. It turns out this was the chief reason my friend wanted me to watch it -- she appreciates the dance parts in the movie.
I do like music, though, so I expected to at least find good music in the film, no less famous for its music and its songs than for its dancing. Leonard Bernstein composed the soundtrack and the songs. The incidental music throughout the film is boring and drips with saccharine. The songs are mostly nothing to write home about. Some are cute ("America", notably, as well as "I feel pretty").
The story is very bad. It is clear that the writer (Arthur Laurents) sought to create a modern version of Shakespeare's Romeo and Juliet. The concept of equating Capulets and Montagues with Puerto-Ricans and whites in 1960s America is valid and promising, but the execution is embarrassingly full of holes. The characters often behave very unreasonably and fail to inspire the necessary suspension of disbelief. The story is one-dimensional, and the characters are stereotypical.
The movie is long (151 minutes), and I had to exert my willpower to weather it all. It won ten academy awards (Oscars) at the time.