Since Neversoft took over for the Guitar Hero franchise, all of the characters had a strange look to them. It was a weird amalgamation of cartoons and caricatures mixed with realistic skin textures and fabrics that made everyone seem too surreal to be in a videogame.
I guess it took the biggest rock band in the world to make them commit to getting the details right. Everyone in the band is recreated in an almost action figure-like essence. Kirk Hammet, Lars Ulrich, and Rob Trujillo are spot on. They look great and seem believable with the help of a few weeks of motion capture. Unfortunately, James Hetfield looks very stoic and very stiff at first. During some of the songs though, his mo-cap sessions pay off and it actually feels like you're on stage at a Metallica concert. Just be prepared to wonder if they replaced the lead singer with Frankenstein the first time the band walks on stage.
I can't imagine it is hard to make a music game based on a band that has over 25 years of material to pull from. Every Metallica album is represented in Guitar Hero: Metallica. From Kill 'em All all the way up to Death Magnetic, there is definitely something in here to satisfy even the most casual of Metallica fans. The breakdown for how many Metallica songs versus all of the other bands that influenced them is about two out of three.
I think it should go without saying that this is as close to the most heavy metal videogame as you can get right now. So, with that, expect to hear other songs from Slayer, Judas Priest, MotorHead, King Diamond, Samhain, and even some newer bands like Mastodon and Machine Head. The Heavy Metal genre prides itself on being gritty and dirty, but I must admit that it is awesome to hear all of these songs mixed in high quality and blasting through my surround sound. It nearly gave me whiplash from headbanging too much.