This album is arguably one of the best albums, if not the best, from Metallica. So much hard work, dedication, and time has gone into this. A lot of classic staple songs, such as Blackened, ...And Justice For All, Harvester Of Sorrow, and One originated from this album, some songs having unique backgrounds.
As far as the sound goes, James Hetfield and Kirk Hammet are not afraid to venture into very distorted and clean areas. ...And Justice For All starts out with a relatively clean sound followed by heavy distortion, One has a jazz sound lasting for most of the first half of the song. It seems very well done. A major disappointment I had was that the bass follows the rhythm guitar... and when you put on 2 guitars (overdubs if needed), quick drumming and vocals, you can hardly hear it. Luckily, it took another step and followed the bass drums more often in the black album, but that's another story.
The musical structure is interesting. The TS switches a lot, mainly 6/4, 13/8, 3/4, 4/4, and a rare 5/4. The tempo likes to switch wildly too. The tempo changes can take you by surprise, so naturally it will be hard to keep a solid beat. Really all I can say.
Finally, most of the songs are awesome. Harvester Of Sorrow is a classic and played at nearly every Metallica show, One is wildly popular for the similarites to Johnny Got His Gun and the complex guitar solo that kicks in after the last verse and the song goes double-time. AJFA is a complicated song that is a blast to listen to and an underrated song, To Live Is To Die, is medelic and may have very few vocals, but it is powerful to hear.
Overall, this album is a must-buy. The only weak points are the bass and some of the songs (Beholder of the Eye isn't really THAT great of a song), but otherwise, it is an awesome song. If you got the money, buy it.