It seems to me that Roger Waters has us all fooled, that this was actually a parody of the highest order. If you watch the interview with him on the bonus materials on the DVD, you can almost see him smile when he discusses the inspiration for this film. It's a film that we read into it what we will. To a small degree, it is autobiographical (most everyone knows about the incident when he spit on a fan during the Animals tour).
Taking that as a leaping off point, he takes the conclusion of the absurdity of the rock star life to its logical end. And it is brilliant. Pink Floyd was simply not the same after the breakup.
It is visually and viscerally stunning. I used to watch this over and over again and it seemed to tap into what I was feeling at the time and it provided comfort, a sense that someone else could relate to the isolation and loneliness I felt, even in the midst of people. I had to replace my vinyl record several times because I listened to it so much. The movie provides eye candy for the songs.
The plot is quite simple: Pink ('by the way, which one's Pink?') is a rock star whose about had enough of the excess and snaps, journeying into his brain way too far. We see the meltdown unfold and follow the transition to something much more frightening, gaining a vision of just how far human vanity can take us. The songs and the visuals form a cohesive whole.
Sure it's pretentious and takes itself too seriously at times - but isn't that the point? It works.
It's one of the darker takes on this life but it nails it brilliantly. You'll find that many of the scenes are bigger than the context of the film. Many of them could be related to events in the political or social sphere of then and today.
It's a bit dated, perhaps, or I've merely gotten older. But the extras on the DVD make it worthwhile, including the video for 'Hey You' featuring footage that didn't make it into the film.