What a great film! I watched it last night, for the second time, and saw alot more - aided by having read some interesting reviews here.
The quality of the script, acting, filming and soundtrack - together with the subject matter (psychosis, alterate realities, social conditioning etc) make it one of my favourite films.
(Spoiler alert)
To begin at the end. Donnie has the enigmatic smile, of perhaps a Higher Soul who has completed his mission, as he awaits his fate from above (aircraft engine/5D). His empathy, intelligence and passion for questioning the 'system' and rationally exposing thereby its contradictory, STS nature makes him an obvious target.
By conscious struggling and eventually overcoming bulling, feelings of isolation, self doubts - attempts at vectoring in different guises - Donnie seems to be doing the Work.
Frank / rabbit may be symbolic of Donnie glimpsing an aspect of his Higher Self. Him being shown one potential reality or timeline - with the ensuing consequences (him killing Frank, his girlfriend dying, but yet exposing a pedo ring etc) and knowing he has the choice to avoid this, by essentially giving his own life.
Very close to the end, we see some of the main characters with their 'masks' removed. The pyschologist, pedo-criminal Jim Cunningham and New Agey Frances Farmer. Their nocturnal, private worlds reveal expressions of anxiety/doubt; guilt/ maybe remorse and deep fear respectively.
Also the character Frank drawing the rabbit, the inference perhaps of seeds of awakening being shared by creative acts within a group or network. One seemingly mediocre act being deeply significant in the life of someone else - if they SEE it.
This film, like others, give us the opportunity to observe and learn lessons about the human condition. But for me, the overriding message from Donnie Darko is one of how our thoughts, words and actions can or do create alternate situations / paths / realities and the responsibilty of their creation and consequences thereof ultimately rest with us. We reap what we sow.