(remainder: this is just my opinion so don't freak out)
I feel Metal is one of the most misunderstood genres out there.
listen to couple of tracks from these albums listed below
Pagan's Mind - Celestial Entrance (Power metal)
Gorguts - Erosion of Sanity (Death Metal)
Overkill - Feel the Fire (Thrash Metal)
Gorgoroth - Pentagram (Black Metal)
Ensiferum - Ensiferum (Viking Metal)
Judas Priest - Sin After Sin (Traditional/heavy metal)
Listen to the musical traits, the way the riffs are presented
though Death Metal is a completely different animal than power metal, both these styles as well as black metal evolved from thrash metal which in turn was spawned from the new wave of british heavy metal acts of the late 70's/early 80's whom were spawned from the early metal acts like Black Sabbath and such. Any way my point is that the subgenres of metal i listed are all interconnected (continued on next post)
