This highly suspenseful film is depicts a great concert by Metallica interspersed with various eerie and destructive scenes. It follows Trip the roadie as he attempts to pick up a package for the band. The unnamed city is Vancouver, by the way, so keep an eye out for familiar sights. Parents should be aware that some images may frighten children, such as a road lined with hung corpses, a few guys who get set on fire (no burns are shown), a character being beaten by an angry mob, a violent riot, a homicidal horseman, a weird voodoo doll type thing, a car crash and a perpetual state of confused terror in the main character, who, it should he noted, becomes increasingly bruised and battered as the film progresses. Aside from that, the concert itself is true to Metallica's form, with strobe lights, explosions, coffins, and the like, as well as several staged accidents. Also, given that they're one of the Big Four of Thrash Metal, the music is themed exactly as one would expect, and features death, destruction, and general mayhem. There is a fair bit of swearing, particularly from a thrasher at the beginning, but it's fairly easy to skip over if you're offended (he's the guy who pulls up in the car to the empty parking lot in the first scene). The only other potential issues are mass destruction of an empty city and Trip's ingestion of an unidentifiable pill.
Now that the bad stuff is out of the way, parents should also know that the band's performance is incredible and inspirational. Although dark, Metallica's music also promotes strength and standing up for oneself in the face of adversity. Trip displays courage, determination, perseverance, and a "won't go down without a fight" attitude. He endangers himself to help a stranger and is willing to give up his own life to save others. While violence is prevalent, it is by no means glorified, and while Trip is willing to fight to when it comes down to it, he does try to avoid involvement in violence if possible. As well, the band is extremely talented and obviously engaged and enthusiastic, and their "average joe" reputation is an inspiration to musicians everywhere.
At the end of the day, if your child isn't frightened by Metallica's music, they won't be frightened by the film. Just play Enter Sandman. If they smile at the mock-lullaby, they'll love the movie.