Castlevania: Legacy of Darkness is a game that is really Castlevania (64) with "director's cut" style additions and refinements. It includes Reinhardt Schneider and Carrie Fernandez's story modes from the previous game, along with two new ones: Werewolf-esque Cornell and Shotgun toting Henry. Cornell and Ortega's journeys take place 8 years before the originals in Castlevania 64.
Otherwise, the gameplay, the enemies, and most of the levels are exactly the same. Players can use the Nintendo 64's Expansion Pak if they feel the graphics need some puttying up.