Why???

Pros:
- Panic-inducing scenes of hopeless carnage that is truly disturbing and upsetting

Cons:
- The presentation is so poorly assembled that it makes the point of the movie feel like it is praising the heinous actions
- Awful character development that fails at creating an interesting protagonist with clear motives and reason for his actions
- Due to the serious nature of the subject matter and the contrasting apathy/silliness presented by the main character, the movie just comes off as cruel and edgy

Final thoughts:

Save yourself the time and watch something better like Confessions. There is actually a point to that movie!