The beginning of the film introduces the charecters and features great dialogue like "Daddy, what does '****ass' mean?" Donnie goes to bed one night, hears a voice(Frank) calling him, so he follows it out of the house to where he first meets the silly rabbit. Right as his sister arrives home, the entire house shakes and we learn that a jet engine fell on Donnie's room while he was outside. The countdown is on and Donnie's world is set to end in 28 days. If you missed more than that, it's not even worth it.
I like the film a ton, but exploring the end of the film still seems to suggest that life will turn out pretty ****ty for most of the charecters anyway, which seems to contradict the overall feeling the end invokes on the surface- that Donnie's fate and destiny will make all the problems that occured afterward right.
For example, Jim would never be exposed, the dance competition will still happen, the plane will still crash, Drew Barrymore will still be fired, and what's her face's mother will still be (likely) kidnapped and murdered.