Heh! I had to check this one out since I did my own imagining of a couple Tolkien songs and Rains of Castamere was something I had in the back of my mind as a sort of litmus test for what makes a solid song in terms of structure and the like.
I'd say this is maybe less blues and more rock.
That said, I actually like where it's going regardless, and it's probably easier to adapt it to rock. To continue on with this project, I'd really lean into the "weeping guitar" upper register, and maybe slow the tempo just a bit so that it still retains its emotional overtone of being a sad song.
I think "Nothing Else Matters" by Metallica would be a good comparison song to draw some inspiration from in terms of making something that still hits hard regardless of the genre change.
Good work.
:)