Assuming that you mean people say this game doesn't feel like a Castlevania because of personal dislikes then it seems more like the other way around. People love to triumphantly exclaim—"This game Castlevania references! The main character is a Belmont, he fights with a whip, obscure reference this, tagged on names that etc etc." Though pretty much all of these points are superficial or aesthetics the game happend to share in common with other titles in the franchise. Just because the main character happens to wield a whip-like weapon which he uses in a manner completely alien from how it was handled in say SCVIV doesn't mean it is a similarity of any relevance. People are making excuses like that up because they like the direction Mercury Steam has taken with the series but just don't want to admit it isn't much like the series they are a fan of in the first place. I really can't stand such kind off retarted fanboyism. It the most dumbest and annoying thing ever.
Actually, it comes down to defining what Castlevania is. Is it having Dracula as the final boss? Well, there goes Lament of Innocence and Dawn of Sorrow and Aria of Sorrow.
Is it spending most of the game in Castle Dracula? Well there goes a bunch of gameboy titles, Curse of Darkness, Simon's Quest and bunch of others.
Maybe it's playing a Belmont? So that takes out most of the games after SotN.
Maybe it's about being able to double back and explore the castle and it's surroundings like a Metroidvania? Well now the original games aren't Castlevania enough to be included
My point is that what makes a game "Castlevania" is mostly a matter of taste. This game is a reboot and uses older references to help get the story going and shape itself. Does it do things differently? Yes. But it isn't any less Castlevania than any other games that have come before it.
After all, while Gabriel uses a whip-like weapon in ways we've never seen before (which can be put down to technological reasons in all cases if we're honest), using it as an example means that every game that included the ability for a character to hold their whip out and flick it around to try and get rid of projectiles is not a Castlevania game.
The game changes as technology advances. The series is no longer a 6 stage, timed 8-bit platformer, and I doubt that we want it to be that. What we love about the series has developed over time, and we're willing to accept games that have absolutely nothing to do with the Belmonts, who are supposed to be the main heroes, as Castlevania.
This is the first game where there was real care taken in crafting it and the story, and where serious design was done on three-dimensional levels. It is different. As different as Symphony of the Night was from Castlevania 3, and as Castlevania 3 was for Castlevania 1, and Simon's Quest from the original, and so on and so forth.
So the question comes back to this. What is it that this game lacks that all other games have that defines them as "Castlevania" games?