The Castlevania Adventure
For a time, American's didn't have a clue about what was going on with the Castlevania continuity. Everyone could understand Castlevania and Castlevania II, as one was a direct follow-up to the other. But then the Castlevania Adventure came out, and it was either a direct sequel to the two previous games, or a distant sequel, or a distant prequel. Bad translations from the Japanese instruction booklets, as well as the normal complete fabrication of story in the American booklets, had this game being another adventure for Simon Belmont. From a certain standpoint, this made sense, as Simon was the hero of the series, so why would audiences expect there to be another member of the clan fighting vampires?
Of course, this was only confused further when Adventure recieved a direct sequel, Castlevania II: Belmont's Revenge, with a story describing the adventure of Christopher Belmont. So where did it fit into the series chronology, and how?
In Japan, the answer was easier, as this game was attributed to Simon's ancestor, Christopher, and took place 100 years before the other games... although, then they got Castlevania III, which also said it took place 100 years before hand and stared Ralph Belmont (Trevor to his American fans). It took a while for Konami to clear all that up. As it stands, though, on its own merits it doesn't really matter if The Castlevania Adventure is a sequel, prequel, ot even a tiny-sized remake -- the game is about a Belmont going to Dracula's castle to defeat the evil within. Some would argue you don't really need more story than that.
On it's own merits, The Castlevania Adventure is a lesser entry in the Castlevania saga. It did manage to take the basic Castlevania gameplay and port it to the underpowered Game Boy system, but in the process lost the standard sub-weapons. The adventure itself was scaled down in size as well, featuring only four stages when even the original game had seven. Plus, the game lacked any sense of fair play. The game is hard. Damned hard. You'll hard pressed to find someone that actually enjoys the game.
In a way, though, without The Castlevania Adventure, we wouldn't have gotten its absolutely sublime sequel, so there's something to be said for that. Adventure graced us with our first, non-Simon hero, and the portable titles only improved from here. While it may not be much fun to play, the game does function as an important milestone in Castlevania history.