Castlevania 2: Simon's Quest
Simon's Quest keeps the side-scrolling action of the first game and adds some RPG elements. You play again as Simon, who's trying to lift a curse put on you by Dracula. The only way to accomplish this is to collect Dracula's body parts, reassemble them, and then destroy him. How quickly you finish the game determines which ending you get.
Simon's Quest is an excellent time-killer, and much longer than the first Castlevania. Its game scheme is similar to Castlevania: Symphony of the Night's.