Castlevania is a "video game," so hearts are fine. However, red crystals in Bloodlines and the N64 games have been an acceptable alternative. One of these two choices are fundamental to the brand's identity, like coins are for Mario. Having them doesn't automatically make it Castlevania, but when so much is changing away from Castlevania's core identity, it allows for a quarter of a baby step into more comfortable territory. (Personally, there's so much that has come to bother me about the LoS saga to this point, that the hearts aren't that big of a deal in the grand scheme. If you had fixed the camera, the level designs, and the combat system ahead of the hearts, I could have lived without the hearts again. But if you're trying to make "Castlevania," it does help to have hearts and/or red crystals).