This film has very well-written script. The characters are nicely-paralleled, simultaneously mirroring one another in their fundamental psychological struggles and diverging in their drives, desires, and ideals. The whole storyline is a psychotic eruption of social inadequacies combined with the ever-present question of whether or not our actions are to be judged by an absolute morality.
With regards to character development, the script may have been better carried by stronger acting -- the internal development was present, but was not sufficiently layered within the characters.
Overall, the film is sufficiently suspenseful to hold the attention of the audience.