Imagine this scenario: a movie is released and wins Academy Award nominations for 4 of the actors in the movie (one-fifth of all the acting nominations allotted for just one movie!), plus one for Best Adapted Screenplay (adapted by the playwright/director from his Pulitzer-prize winning play). One would think this movie would be a lock for a Best Picture nomination, no? Well not this year. "Doubt," adapted from his play and directed by John Patrick Shanley, won nominations for screenplay, Best Actress for Meryl Streep, Best Supporting Actor for Philip Seymour Hoffman, and Best Supporting Actress nominations for Amy Adams and Viola Davis. It's certainly one of the best movies of the year, and yet for some reason, it wasn't considered for Best Picture. It seems like that elusive "buzz" is key to nominations, and Doubt didn't get any of the best picture categories in the Golden Globes or other earlier awards, so I think didn't gain the momentum it would have needed to take the 5th spot that The Reader took, and many thought Dark Knight would take.
Though I don't have an explanation as to why, I can tell you that it's a great movie. Phenomenal acting, great writing that continually draws you in, and a story with compelling themes. And all of it told in a way that never feels like it was adapted from a stage play. So I think you should see it, and then tell me what you thought.