I'll get one thing out of the way as we begin this review. Your enjoyment of Metallica's music will be directly proportional to how much you will enjoy this game. It is a love letter to the band, in video game form. Dozens of Metallica's songs, from early in their career to their most recent tunes, are included. The game is packed full of bonus features like motion capture videos, pop up trivia tracks, interviews, and many more.
It is clear that the folks who made the game are fans of Metallica, and there is an extra level of attention to detail, a sort of loving, go the extra mile polish, that was missing from previous Activision Guitar Hero titles. I've not played GH Aerosmith yet, but I have played the AC/DC Rock Band pack, and GH Metallica outshines that effort in almost every way. Whether you prefer disc based releases or DLC, you cannot deny the value of the extras that make GH Metallica much more than just a new set list.
As far as new features go, GH Metallica is not revolutionary by any means. A few little gameplay tweaks have been implemented. There is now a star meter, so you can tell how many stars your performance has earned even as you play. Individual rock meters are a welcome addition as well, so you can tell who is keeping up with the head banging and who isn't. Another small change is a bigger visual indicator when the band is about to fail: the edges of the screen turn red and blink. Each of these changes is minor, but certainly worthwhile.
By far the biggest change is the addition of a new difficulty level, Expert +, on drums. This allows you to use double bass pedals just like Lars himself. (The double bass pedal and splitter cost around $20, incidentally.) I'm not even close to being good enough on drums to test it, but it's a cool addition for those whose calves can take the strain. It's odd that Expert + is available for drums first, and not guitar. Given the fact that guitars have been available in these games from the beginning, a new difficulty for that instrument seems to make more sense, particularly for a game featuring axe virtuosos like Kirk and James.
The co-op elements are particularly strong in games of this genre, and GH Metallica is no exception. If anything, being able to play as an established, arguably legendary "real" band adds to experience. When playing non-Metallica songs, all the familiar Guitar Hero characters are available to use, but the majority of the game is spent with the perfectly captured likenesses of Metallica themselves on stage. The feeling of really being at a Metallica concert, surrounded by thousands of screaming fans, is addicting. Many of the venues are based on Metallica's album covers; I especially liked the Master of Puppets stage. It may sound strange, but not being a random character, and instead being in Metallica's shoes, makes you really feel like a titan of heavy metal, much more than any other full band game, in my experience.
There are a few glaring weaknesses in the co-op, though, that mar what might otherwise be a perfect score. The biggest, one that is a leftover from GH World Tour, is the fact that you cannot use star power to save a bandmate who is failing. Players accumulate star power in a shared pool, and anyone can use it once it becomes available. This does have a certain cooperative feel, I suppose, but it doesn't compare to Rock Bands "deploy to save a teammate" mechanic. Imagine playing Castle Crashers or Gears 2 without being able to revive your partners; it would feel far less like co-op, and more like simultaneous single player. That is exactly the problem with GH World Tour, and unfortunately it plagues Metallica's game as well.
Adding insult to the injury is one of the most bone headed achievement booboos in recent memory. My son and I played through the entire campaign over two evenings, and when the last song was played, "Nothing Else Matters", the co-op campaign achievement, popped up. For me, that is, not for my son, though we played entirely together. After doing some research, I learned that only the band leader earns the achievement! Ludicrous, isn't it? This is a minor detail, and affects only those who care about achievements, but still, it's irritating.
For music games, in the end, it's all about the music. Metallica is a natural fit for the Guitar Hero franchise, since there are three, well, guitar heroes, and a drum hero, in the band. As a fan of Metallica's music, I love the game; it's that simple. Beyond just the gameplay, the bonus features are enjoyable, as well. These extras are what will make or break these band-centric games, I think. Games like The Beatles Rock Band and Guitar Hero Van Halen should take the history and behind the scenes features to the next level. Hopefully, Activision will realize the weakness of the co-op in their titles compared to those of Harmonix, and we'll all be able to enjoy even better full band games in the future.