This came out in Dec 11 and I found out it existed Apr 12, so I'm not the greatest Metallica fan checking their news everyday. But I have a few of their albums, my favourite being Death Magnetic.
This is well worth the purchase, esp as I downloaded it for £2.79. I haven't checked the total run time, but other reviews say it's approx 29 minutes.
Anyway, it's very good! The first time through I really enjoyed the music but found the tunes i.e. the tunes Hetfield sang - and the lyrics - to be a little sub-par, even irritating. But by the 3rd run-thru, I'm really enjoying it, and the music gets better and better.
If you're a big Metallica fan, you've prob already got this. If you're the kind of Metallica fan who has some of their records and only REALLY likes one or two of them, then I would still recommend this (esp if one of those was Death Magnetic). Parts of it are really very good indeed!