Guitar Hero: Metallica ESRB listing gives us more details

Content descriptors: Lyrics, Mild Suggestive Themes

Rating summary: This is a music and rhythm simulation game featuring the heavy metal band Metallica. Players can perform songs using on-screen avatars with various instruments. Players simulate playing guitar, bass, or drums and are scored based on the accuracy of notes hit. Some song lyrics contain expletives (e.g., “damn,” “bastard,” and “b*tch”) and sexual references (e.g., “Mommy’s little monster had sex at 15″ and “sweet and timely whore, take me home”). Some song lyrics also make references to violence (e.g., “We’re gathered here to maim and kill” and “I got a gunsight trained on you”). Some of the players’ outfits are low-cut and revealing, while tattoo designs depict women in provocative poses and clothing (e.g., a fantastical succubus with cleavage and panties).