"Of course, there are many that would argue that would not be a bad thing as Donnie Darko can be a very inscrutable film.
It combines elements of the angst of not fitting into high school society, the cultural and political climate of the late 80's and time travel; Yup time travel. The film slides through conventional genres in a manner that is almost haphazard making it hard to easily classify much less digest in a single viewing. Donnie Darko works on multiple thematic levels though its core could best be described as science fiction. For those who have little tolerance for ambiguity, this is probably not a top recommendation, but, if you are so inclined, Kelly's film delivers an extremely satisfying emotional/psychological experience (though I would not call it a thriller) with precise mood and setting even if it is not easily understandable.
I should clarify that my comments are about the theatrical version as Kelly revisited the film only three years after release for a director's cut. The later version includes 21 minutes of additional footage (including new special effects), changes in editing and differences in the sound mix both with the use of music and ambient effects.
What I mentioned above about the film being inscrutable is exactly what Kelly wanted to remedy as he thinks the central plot points about Donnie should not be up for debate and has a definitive vision of how the film should be interpreted. Thus his director's cut removes much of the opaqueness of the narrative (making it more mundanely offbeat) and for my tastes has too much spoon feeding that in the process of clarification destroys the beautiful mystery the theatrical version delivers. Thankfully Fox had the foresight to not force us to choose as consumers and provide both versions allowing you to make your decision about which is preferable (though I would definitely recommend starting with the theatrical version)". Source: www.thehdroom.com