Used to be, but in the last decade it's not as succesful as Metal Gear Solis series though.
The entire series of Metal Gear has sold over 66.4 million copies while Castlevania has sold around 24 million copies across its lifetime.
But if you're a Castlevania fan, be happy then.
After a decade of just releasing collection, this year it will get a new game: Castlevania: Belmont's Curse.
It is kinda difficult squeezing fresh content out of Dracula all the time.
Dracula rises and causes trouble.
Belmont rise to the challenge, despite bad public relations.
Belmont slays Dracula, Belmont is either regarded a hero, or no one cares.
Hundred or so years later, Dracula resurrects, rinse and repeat.
I know Dracula is a public domain villain, but why not let some other great evil challenge the Belmonts every now and again?
What about, a London adventure that still has a vampire overlord, only instead of a grand castle and an army of monsters, this vampire is
Lord Ruthven. He claims to be older, more powerful than Dracula, only instead of sitting high in a castle, he walks amongst the aristocracy and manipulates them into his bidding. Thus the Belmont can't just whip his way through monsters to get to Ruthven.
Or, for the sake of traditional gameplay, perhaps Lord Ruthven set up his base of operations in the famous Catacombs of Paris, turning the catacombs into an extended dungeon-underground fortress like place.