I hadn't heard anything about it before seeing it in the new releases section of my local video store. It's rated #23 in the top 250 movies of all time at the Internet Movie Database, so it's not unheard of, and basically a lot of other people like the movie, too.
The movie is the story of youths living in the City of God in Brazil, told from the 1960s through the 1980s. They live in poverty and take different paths to try to escape the lives they've been given. But it's not just the story that's fascinating, but the film itself, from the first few minutes of a high-paced chicken race and throughout, the viewer is hooked.