We totally need to jump onto making the metal version of this now that it's finished!
When I listen to the piece you've made overall with the vocals, piano-work, organ-work and ambience-work, it reminds me sometimes of a more 'positive-sounding' (in mood) Evig Natt style track at certain points (from around their work on the 'I Am Silence' album).
I think if I was to nitpick just to try and get at least one constructive piece into the comment section, the piano playing on the lower octave at around 2:14 lost abit too much of it's mid-presence. Automating an EQ to boost it's mid-freq tones specifically at that segment of the track (then disabling it after that segment's finished) could be beneficial in the future if you're looking to do a future revision.
Gets a thumbs-up from me overall!