You gotta be kidding me about Metallica.
They have changed their style so much.
They started making just really awsome music in the
80s and continued making it with a big change of sound in every new album.

Then they made Black album in 1991(I think) which was a lot more commercial.

Then they started making "mtv material" until St. Anger which also had a completely new sound.

You may not like them but all their songs do NOT sound the same.

They have changed more then most bands I know of.
(And for the worse. They should've quit after And Justice for all.)