Personally, I think Metallica, as a band, their greatest influence and accomplishment would be One. It brings together great guitar riffs, astonishing solos and arguably the first breakdown ever recorded in Metal. Nowadays, you hear breakdowns in all the metal and metalcore songs and in my opinion it is what brings out that element of metal that needs to be there. Take away the breakdown in One and it definately isn't the song it's meant to be.