Metallica
Kill 'Em All - Thrash metal at its core, taking inspiration from the NWOBHM bands like Mercyful Fate and Black Sabbath, this comes ripping onto the scene with no remorse 
Ride The Lightning - A heavy metal masterpiece with a little more melody, including the ever popular Fade to Black and the instrumental Call of Ktulu.
Master Of Puppets - The perfect album IMO, with streams of melody and and metal that could make anyones bones quiver. Welcome Home (Sanitarium) is the highlight for me (seeings how its my favorite song ever).
…And Justice For All - The 4th masterpiece in a row, with the haunting One and crushing Blackened. Could it get any better than this? Well maybe not according to some…
Metallica - Known to fans worldwide as the black album. Metallica fans of old felt betrayed by the ballad Nothing Else Matters, while songs like Enter Sandman and Sad But True remained true to form heavy metal. This record would shoot the band into a worldwide major success and led them on 2 and a half years of touring.
Load - The new era of Metallica that was met with mixed emotions by fans of old. Gone are the thrashing tunes of Puppets or Justice, and songs like Hero Of The Day and King Nothing are the new, lighter approach of Metallica.
Reload - Continuing the “Load” era of Metallica, still we have no classics as in the 1st 4 albums, yet songs like Unforgiven II make us wonder if they will ever go back to the old days.
S&M - Some people would say Metallica has gone mad, preforming a virtual “greatest hits” set with an orchestra. I myself thought it was a thing of beauty, unmatched power and energy. Some would have you think this was the end of Metallica, and it was almost true, though not due to this album. There were many many problems within the band that had existed for the better part of a decade, and few years later they would lose their bass player and the lead singer went into rehab. It looked bleak untill…
St. Anger - Metallica was definitely back to the form of the early 80s. Rather then revisit that style though, they re-invented it. The entire album is on speed, no melodys, no ballads, no solos, just pure raw aggression. The boys also added a new bass player who brought an energy to the band they haven’t seen since their 1st one.
Metallica has definitely evolved, for better or worse, but their fanbase continues to grow despite the few dissidents who have abandoned them for changing. All in all I think Metallicas evolution is great, and I also think their next album will show how rejuvinated the boys really are.