Castlevania: The Adventure for the Game Boy. Why? Mainly because of the really horrible jumping. The game actually requires you to do some pixel-precise jumps at the end of Stage 1. Now, there are no bottomless pits at that particular part, but you have to do pixel-precise jumps later on as well, and those are above bottomless pits or instant-death spikes. I am not kidding. Furthermore, the game has a tendency to drop your inputs. You also lose your upgraded whip as soon as you get hit, which pretty much isn't present in other Castlevania games (in those, you only lose your upgraded whip when you lose a life). The only good part of this game is the music, which sounds really good for a Game Boy game released in 1989, in my opinion.