Castlevania II: Belmont's Revenge
If The Castlevania Adventure was an attempt to shrink the Castlevania experience down for the gamer on the go, Castlevania II: Belmont's Revenge (commonly referred to as simple Castlevania Adventure II) was the first time is was actually done right. Commonly deried as too hard, Adventure was a flawed game that no one really liked. Adventure II, though, took the few elements the first game managed to parlay properly to the Game Boy, and then improved everything else.
Setting the story 15 years after the events of the first game, Christopher Belmont has to go in search of his missing son at four mysterious castles. The player gets to choose where to go, and in what order the castles are handled -- this isn't just branching paths, but a Mega Man-style freedom to explore. For series fans, this was a truly interesting freature (and one that, sadly, was not used again in later titles).
Unlike in the first game, Christopher Belmont actually gets to use the classic sub-weapons. The dagger and axe both make appearances (although in Japan the axe was swapped out for the cross), and the axe comes in very handy against some of the larger bosses. Additionally, unlike in the first game where any hit would reduce Christopher's whip-power, only specific attacks (the orb spit out by weird hand-demons, Punaguchi) would cause the whip to downgrade. This makes the game effectively easier and more manageable.
Not that the game was a cake-walk. Even if the player accessed "Easy Mode" on the password screen, the game still took concentration and skill. Playing through it on "Normal Mode" proved much more difficult -- although not as punishingly so as with the first game.
The game would prove to be the last official entry in the series for Christopher -- the next Game Boy game starred Sonia Belmont (another under-utilized hero), and Christopher's only other adventure was the "remake" of the first game, Castlevania: The Adventure ReBirth. Although not considered one of the top members of the clan (he didn't get included in the "Greatest Five"), Christopher had a fitting send off with Castlevania II: Belmont's Revenge.