Look up some screenshots of Super Ghouls 'n Ghosts or Actraiser. They look almost identical to those games, which were originally accomplished on 16-bit machines. Impressive stuff.
It's super interesting that someone remembers Jim Power enough to demake it into an NES game. I've seen this game on a Game Sack episode long ago and gave it a try, it has amazing graphics and wonderful music but the gameplay kind of sucks. This was originally an Amiga game and it doesn't really hold up, which is apparently common for Amiga.
Edit: Apparently Piko Interactive made an Enhanced Editon, I gotta try this.