What I like in the Metallica of the 80s is there are strong
N.W.O.B.H.M influences but the guitars don't sound ridiculously high-pitched as in Iron Maiden for instance, Metallica could really border on the prog-metal (there are palpable classical music influences in several songs) but they don't cross the line (maybe because of their punk and hardcore influences), their music is massive, especially on Master of puppets (well off course that's why it was called thrash metal
).