My quick review.. (bear in mind that I played single player guitar for the time that I played it.)
First off, I'm not the biggest Metallica fan ever, but I love quite a bit of their songs. I was hyped for this game and picked it up at midnight. It seems like the developer's hearts were in the right place while making this, but it just feels.. off.
First off, the presentation, as noted, is top notch. You really feel as if they're playing on stage, and it is, without a doubt, the best a GH game has looked. The unfortunate part of this is that you're supposed to be paying attention to the notechart. This could've been remedied with a mode similar to Rock Band 2's axed "Jukebox" mode, where there'd be no notechart or anything, you'd just get to watch the band play. I kept getting distracted by pyro and crazy antics and I would miss a note or two.
Secondly, everything's unlocked! I know what they were thinking.. they realize that Metallica songs are not easy to play and therefore they shouldn't make people play through career mode to unlock songs. Again, the problem: It sucks the fun right out of it! After an hour or two of playing through the initial batch of songs that you want to play, you're not really going to want to play through career mode. Any satisfaction or sense of accomplishment you could've gotten from finally nailing the solo on that one part of a song to unlock a song you've been waiting to play is stolen.
The live performances and behind the scenes mo-cap is cool, but after about two hours, I feel like I'm done. I have nothing to unlock, it's unlocked for me. All of the live performances and behind the scenes videos are unlocked after you play the first two songs in career mode. There are four or five more locked videos. I'm assuming they pertain to the career mode and aren't Metallica music videos or live performances or anything.
Don't get me wrong. The songs are awesome, the notecharts are a little underwhelming on expert (the only one to give me difficulty so far was "All Nightmare Long" at 77%).. but unless you're a HUGE Metallica or Guitar Hero fan, rent it or pass altogether. This will probably wind up on my tradelist soon.
//edit: Also, "Turn the Page"'s chart is weird as hell.