This was not the first Castlevania game to let players play as Alucard, he was previously available as a spiritual helper in Castlevania III: Dracula's Curse.
Reissued for the Sega Saturn with a new area that wasn't in the Playstation version. This version has never been released in America.
First Castlevania game to separate from the "stage-by-stage" gameplay of earlier games, and create a more Metroid-esque play experience, which also featured RPG elements (leveling up, equipping new stuff, item usage, etc.)
The game's equipment/item use system worked differently than later "Metroidvania" style games. Items had to be equipped to be used, and a piece of equipment could be put in either hand (you could have a shield in one hand a sword in the other, two swords, two shields, etc.) This was not repeated in later installments.
On the arch of the corridors that connect the stages, a circle can be seen with the letters "CD" engraved. Fittingly, this could be a reference to the fact that this game was released on CD. It is also an allusion for the antagonist of the series, Count Dracula.