I like how Gus Van Sant played with time in this film. When in a scene focusing on a character, other characters move in the background. Then, he jumps back in time to follow that character, and eventually goes right back through that scene but from the other perspective. I really liked how that worked.
The pacing seems pretty slow, but I think it works, because the long shots add a much more realness to movie rather than quick cuts. You see the characters as they move and interact with people, even just the waves and nods.
Ultimately, the movie doesn't do anything to answer any of the questions regarding school shootings. It doesn't justify or attack events such as Columbine, but instead just puts you there. But, I don't think the point was to explain anything. It wasn't meant to offer any sort of insight or understanding.
The movie itself feels like an experiment in a style of story telling, not necessarily telling a story. The style of camera movement and pacing creates a very calm atmosphere in this school where a pretty horrible thing occurs. But in the chaos that ensues when the students start opening fire is counterbalanced by the slow, fly-on-the-wall method of story telling.
I liked it, not so much for the story, but for how the story was told. I think it was a very beautiful movie that showcases how playing with pacing and shot lengths can really alter the mood of a movie, even when something terrible happens.