The first two games are damn good also. I think I have a cart of the first game. :O Second one's a little more allusive (haven't tried hard, though). The NES game is almost a remake of the first.
The SNES game is definitely the best of the bunch. I'd want a sequel, but I'm afraid it would be really fuxed up and not nearly as good.
Gargoyle's Quest/Demon's Crest is an example of a spin-off series being better than the series it branched from. In my opinion, at least. Though I probably only say that 'cos the Ghosts'n Goblins/Ghouls'n Ghosts games are so damn hard.