The themes (SPOILER)

The premise isn't juvenile at all, as some clueless critic suggested. In fact, it reflects real life as the potentially fatal curse for loose sex is akin to venereal disease, albeit spiritually rooted. It's the casual-sex-equals-death motif of slasher flicks but deeper. The "monster" in the movie represents the repercussions of meaningless sex, which may be physical, psychological or spiritual, but there is a price to pay. Two of the characters are childhood friends and their union is the antithesis of casual. Note the subtle yet potent climax.

In addition, there are interesting subthemes to be gleaned, like the safe suburbs vs. the danger of the rundown inner city.