Hoop Dreams is one of the best documentaries I've ever seen. I first saw it fifteen years ago after seeing it reviewed on Siskel & Ebert.
Here's the review that got me to invest 3 hours in Hoop Dreams, one of the best investments I've made.
Roger Ebert looks back upon Hoop Dreams on his blog. Here's an amazing detail I did not know until today. I still can't believe it.
The way seemed clear for an Academy Award as best documentary. Then a shameful thing happened. It wasn't even nominated by the Academy's documentary committee. We learned, through very reliable sources, that the members of the committee had a system. They carried little flashlights. When one gave up on a film, he waved a light on the screen. When a majority of flashlights had voted, the film was switched off. "Hoop Dreams" was stopped after 15 minutes.
If you've never seen Hoop Dreams, do yourself a favour and get a copy. Like Roger said, you owe it to yourself.