I finally watched the copy of Donnie Darko Lumi gave me. It's kind of like 12 Monkeys, in that it's a freaky speculative film with a crazed if not insane protagonist, and manages to build up an entire mythology around the story without answering every question. (Some of the DVD extras explain a bit more, so you might skip them.) The period 80s atmosphere is great without beating you over the head with it, as is the music: it's seriously 80s, but it's in the new wave vein that I'll listen to even today.
So, basically, it's a wonderfully disturbing movie reminiscent of 12 Monkeys, which I also loved. A++++, will watch again.