It's the true story of serial killer Jeffrey Dahmer in his high school days as told by his friend who created a graphic novel about the experience etc. etc. , but that is not what makes this movie great although it is a part of the reason. It's just a gut-wrenching realistic portrayal of the horror of a young man not fitting in at high school and gradually losing himself to madness.
Primarily I would have to say the screenplay is brilliantly written, but the cast is somehow weirdly perfect, young douchy-haired Disney child star Ross Lynch just proved himself an amazing actor on a par with any of the best, still surprising although it shouldn't be, there have been so many Disney Kids who have grown up to do seriously good adult stuff now.
The rest of the high school cast is great too but who stands out is Anne Heche and Dallas Roberts in the roles of the parents. This is the best acting I've seen from Anne Heche. I've always thought she was an underrated and under-utilized actress capable of more and she brings the more here, and ironically-named-Houstonian Dallas Roberts is brilliant as the awkward dad trying to cope with his weird son (you will know him from the Walking Dead).
More than anything, the soundtrack is just absolutely perfect for the subject matter.It's not your typical period-piece type of soundtrack, just throwing out the Top Ten list from that year, it has some songs that you will likely only find on dusty vinyl in some dusty Rust Belt garage. Hauntingly obscure and evocative of the time and place, it's one of my favorite soundtracks ever.
On top of everything, this movie was filmed in the actual house that the real Jeffry Dahmer grew up in. It gives me chills just re-watching it. One of the beast horror movies I have ever seen, without any of the gratuitary violence or special effects.
This is a masterfully crafted film and sure to be a cult classic many years from now.