A great addition to the Guitar Hero games.
The music is great, firstly. Metallica are the perfect band for the game, with their hard metal songs.
The setlist features the best Metallica songs recorded. From Enter Sandman to Master of Puppets, you can't help jumping around, rocking out. Metallica chose the guest acts, and they chose fairly well. Chosing songs like System of a Down's 'Toxicity' and Mercyful Fate's quite mad song 'Evil', Metallica know what the GH players want.
Second, the character designs are great. All four Metallica players look great. They have also put more effort in. When you get to a certain number of stars across the songs, you earn the classic version of the character. For example, if you play guitar (Kirk Hammett) and earn 100 stars, you earn the classic model of Hammett.
Third, they have raised the difficulty. Players complained about the toughness of GH3 so the GH team made Guitar Hero Aerosmith far too easy. They've now made it more difficult again so all hardcore players have a challenge.
It's one of the best Guitar Hero games to date and would be enjoyed by all rock music fans.