I'll never understand why some people consider the NES Ghosts N Goblins harder than the arcade or PS1/Saturn/PS2/PSP ports. The NES one is a glitch filled mess, the arcade one has it's share of glitches too, but they don't seem as bad (including being able to skip the second dragon boss later in the game via a trick of going left as the boss music starts, make sure you don't "see" the dragon as then the trick won't work). I played the arcade GnG just this past week, got to stage 5 in 1 credit, wasn't even close to finishing it though as you must do 2 loops for the Happy End (first time I've seen a machine for it in over a decade and a half). Then the game continuously loops after that. Enemies seem to swarm you much faster and more often in the other versions, not so much in the NES or GBC versions.
To this day GnG NES remains in my collection, but I'll play the Saturn or PS1 ports long before the NES one.