Dahmer is portrayed quite tragically in this, which I found to be pretty captivating. I mean it would be easy just to make him seem like a psycho maniac monster, but instead they chose to portray him in a slightly softer, tenderer, almost sympathetic light, which I found quite intriguing. Jeremy Renner did a pretty good job as well, I thought.
Renner is damn compelling. I like the statement it makes about love, that it is not always the responsible path and that it isn't always what is best. They make Dahmer romantic which makes the character tragic. I think this is true though, I remember him saying (in real life) that he did what he did, "so they would never leave me alone", I found that statement to be one of the saddest things I've ever heard.