I will start by saying I know next to nothing about death metal.
This is excellent, the style is irreproachable, each new traits (36 of them ! ) come with a bit of lore and mechanic, the change to 3D6 to allow for a 666 to be rolled is very smart. And when you finished reading about all the thing for the players and already ready to put the highest rating, there is also a section fo Refere, and then some lore with a dozen organisation.
The ambiance seems a lot darker, more like a cthulu or other horrors game than the militarist vibe of FIST, with demons and otherworldly horrors.
The trait seems to go a little on the high end for the power end impact on game, but FIST already come with very powerfull trait, so it shoudn't be problematic to use in a standard game (and the game has the little box with advice to the refere, so it's even more easy to integrate this content in the standard game ! )
5/5