I've never seen the full movie or the full stage musical - in both cases, just individual numbers out of context. As I understand it, they're very different, and that's largely why the movie flopped - it cut a lot of numbers, wrote a lot of new ones, re-contextualized some of the other songs, and sidelined the gay characters. That annoyed fans of the stage musical, who were a lot of the early ticket buyers, and the word of mouth ended up being terrible. Critical reception was more mixed (i.e. not a rave, but not a pan).

Part of the reason I was interested in looking at just the opening number of the movie is because it's emphatically in the medium of film, and would be a sequence very much in the control of the director rather than the screenwriter - a visual thesis of how the movie is going to present dance images, rather than how it's going to handle plot.

It's cool that you got to see it as a kid with your grandmother. I know that my mom (also a performer) loved/loves the stage version. The actress who doesn't get cast but did clearly get cast is so metatextual.