If you don’t want to use PKG files, you have two other options to play Guitar Hero: Metallica on PS3:
The .pkg file contains the following critical components necessary for execution:
Before proceeding, a critical note: Guitar Hero: Metallica is considered —the official licenses for the songs (Metallica’s catalog, Foo Fighters, Slayer, etc.) expired years ago. Sony no longer sells it, and Activision has no re-release plans.