Most plot descriptions of this film push you in the wrong direction and can go suck a fuck. They always sound too weird and wacky. This is an 80s retro high school movie, mixed up with a whole bunch of social commentary, philosophy, atmospheric terror and a lot of laughs. Jake and Maggie Gyllenhaal play a brother and sister in a regular middle-class American, Bush Snr. voting, suburban 2.4 nuclear family. He (Donnie) sleepwalks, takes pills and sees a $200 per hour shrink (Katharine Ross, the beauty from The Graduate) to talk about his imaginary friends and dreams. It's a month away from Hallowe'en, but already freaky things are happening.
Patrick Swayze atones somewhat for his 80s fuckass movies with a perfect character acting role as Jim Cunningham, a self-help neo-evangelist, preaching his own gospel of Love not Fear. Drew Barrymore is Donnie's English teacher, who tells a new female student to sit next to whoever she thinks is the cutest boy in the class. The private school PTA palpably hums with Republican values.
Writer/director Richard Kelly creates some startling cinematic beauty, right from the opening shots when Donnie wakes up in the middle of the road, on top of a hill somewhere in Virginia (or near Washington D.C. anyway - they watch a Redskins game on the TV). He plays with timelapse and computer animation, and relies on a subtle soundtrack to set the tone.
Nugget: the Director's Cut has recently been released. I haven't seen it; but I don't think you should try to retouch a movie that is so sweetly balanced. It's a thing of beauty.