
I like Ghosts'n Goblins. You probably don't. That's okay. I grew up with it.
Way back when, in the days before video game magazines existed and dinosaurs lived in peace with us simple cavemen, everything you knew about a game came from the back of its box. Ghosts'n Goblins sold itself to six-year-old me pretty easily. "Seven levels!" it said. Zombies! Dragons! Giants! Endorsed by Captain Commando himself, whoever that is! And look at that awesome screenshot (from the graphically superior arcade version, but whatever)!
When I got home and played Ghosts'n Goblins for the first time, I was humbled.

This was a far cry from the games I was used to playing. Super Mario Bros. at least had the courtesy to start off easy and then gradually ramp up the difficulty, but Ghosts'n Goblins was different. In Ghosts'n Goblins, zombies swarm you. Birds fly at your head, hungry for tasty head-meat. Man-eating plants spit poison at you, and then there's that damned red devil, who seems to dodge everything you throw at him and takes a million hits to kill. And on the off chance that you do kill him, you're rewarded with a series of precision jumps over instant-kill bottomless pits.
This is just the first half of the first level.
Gamers weaned on stuff like Super Mario Galaxy today will probably find Ghosts'n Goblins to be even more difficult than I did at first, and will likely give up after their first few attempts. When your game library has less than ten games in it, though, you tend to play everything you have as much as possible. Such was the case with me and Ghosts'n Goblins. The game beat me down, sparked endless frustration, and probably caused many of the mysterious bite marks on my original NES controllers.
In the end, though, I learned to appreciate its difficulty. I learned skills in Ghosts'n Goblins that made me a better player in other games. It helped me in recognizing enemy patterns, and my reaction speed in general improved by a huge amount.
Nowadays, after playing Ghosts'n Goblins off and on for almost 20 years, I'm finally able to get to level 3 without using a continue.
Sometimes.

All considered, though, Ghouls'n Ghosts on the Genesis makes for a much better introduction to the GnG series than either its prequel or its sequel (Super Ghouls'n Ghosts, for the SNES), since its difficulty level is much more considerate to new players. You should try that one out first, if you've never touched a GnG game before. I'd also recommend Super Ghouls'n Ghosts over the original Ghosts'n Goblins for the same reason, even though it's actually a much harder game overall.
The fact that Nintendo chose to release Ghosts'n Goblins only after both of its successors hit the Virtual Console is telling. Ghosts'n Goblins is a rough game, and you should only invest your five dollars if you're prepared to train to be a better gamer.
As can be expected, YouTube is happy to embarrass us all by providing a video of someone completely destroying Ghosts'n Goblins in one life. It also hosts a related video of some braying jackass with a speech impediment ripping off the Angry Nintendo Nerd, but such is life.