Considering the other works by Richard Kelly, I think it’s safe to call “Donnie Darko” a happy accident. It’s a successful exercise in style, with a fine cast, and a fantastic soundtrack complementing some really interesting cinematography. But what works best is the way the film leaves you wanting to know more. I originally thought this lack of clarity was deliberate and brilliant on Kelly’s part. Having seen (or attempted to watch) other Kelly films, and witnessed his attempts to cash in and “add clarity” to the original, I’m convinced “Donnie Darko” is a rare example of art that succeeds because of its failures. By editing out the most convoluted and non-sensical science fiction explanations of the story in the original, “Donnie Darko” focuses on appealing characters, and let’s the audience fill in their own blanks for the “plot.” The background is sooo complicated, and the film is so lacking in clarity, that it provoked multiple theories and discussions of what the film was really about - Reverse “It’s A Wonderful Life”, Donnie is Superhero, Tangent Universes & Artifacts. Which was all great. Until… ya know… the director tried to actually answer the questions. And then there was a big collective “meh.”
I’d forgotten this, but I saw Donnie Darko several years before I saw An American Werewolf in London. When I did get around to seeing the latter, I was surprised by 1) how well it had held up and 2) how obvious it was that Donnie Darko had ripped it off.
One line made the entire movie worth watching-
“Somtimes, I doubt your comittment to Sparkle Motion”! - courtesy of Kitty Farmer
I am a big fan of Beth Grant, the actress who played Kitty Farmer! I had the pleasure of meeting her earlier this year when I was in L.A. Even though she has played more than 200 television and movie roles, this is the one people mention the most! She has even recorded it several times on outgoing voicemail and answering machine messages…including mine! 
I think it insists upon itself.