Incredibly dark, sometimes comic, and engaging, Killer Joe is an uncanny film about uncanny people. Set in a Texas trailer-park, the film delves straight in to unlikable, shallow, dumb characters, and gives us a familiar premise, killing for insurance money, and does not look back.
Killer Joe has a lot working for it. For one, Matthew McConaughey's performance of a nefarious and sadistic cop/hired killer, with a vague sense of self-awareness, absolutely makes the film. He inhibits his character completely, and brings a very engaging presence to his role. The other performances are strong in their own way, with Thomas Haden Church playing good comic relief.
The film is also composed well, with great world building. We see an environment as it truly would be, with excellent photography and scene construction that present us what feels like a very authentic take of rural/trailer trash Texas.
The script is strong from the standpoint that it has good dialogue, and generally does a strong job of incorporating some comedic elements. However, I felt the third act was lacking. A character is only vaguely referred to and introduced, but is an integral part of the later developments. We are never afforded the chance to understand him, which undermines the later twist. This is a problem with many of the characters, with too shallow characterizations. This is perhaps intentional to some extent, but more balance could have been shown between giving us back-story and motivations, while at the same time acknowledging that thought didn't go in to a lot of their actions.
It's not quite a Cohen brothers film, but a strong dark comedy nonetheless.