in no particular order; some are recent rabbit holes I've enjoyed

• doom metal
• death-doom
• gothic doom
• NYHC
• grindcore
• old skool emotional hardcore before it got popular
• horrorpunk
• death metal
• thrash-death
• progressive metal
• dark power/fantasy metal
• industrial metal
• cybergrind
• nintendocore
• nerdcore hip-hop
• chiptunes (as in made by hacking electronics)
• aggrotech
• darkwave
• death rock
• intellectual & political hip-hop
• jazz-hop
• rez rap
• dirty / southern blues
• dark jazz
• freeform / improv jazz
• symphonic deathcore
• symphonic black metal
• symphonic doom metal
• symphonic gothic metal
• ... and much more