It feels like a Castlevania game to me.
Now that that's out of the way, I will tell you how I feel about the game thus far:
1. Gameplay: 8 out of 10. The game does have a similar play style to other games such as God of War, Shadow of the Collossus, etc. But it works. Gabriel has a Combat Cross rather than a whip, but the devs decided to give fans a throwback and named it Vampire Killer. Which was the name of the whip the Belmonts used to kill vampires and such in earlier games. Now it does have flaws. I have been frustrated a couple of times while concentrating on killing a group of bad guys, and suddenly the camera cuts away and shows me something else, then switches back again and I got some werewolf damn near clawing me to death. The titan fights can be quite enjoyable. It is reminiscent of Shadow of the Colossus it's true, but I for one am happy they are doing games like ole SotC again. Now I may have just proved the naysayers right by saying it borrows from other games, it is taking the series in a new direction at least. They can't make 2D sidescrolling Castlevania games forever.
2. Graphics: 10 out of 10. Very little here to complain of. The new art style gets away from the anime and seems more medieval. Which is appropriate considering the series takes place in medieval Europe. Really this is just a matter of taste, and I personally love the graphics.
3. Music: 10 out of 10. High quality music that creates a really appropriate atmosphere.
4. Story: 10 out of 10. Each individual segment of every chapter begins with a narrative. Patrick Stewart himself put in long hours just so he could narrate this. Plenty of things going on.
5. Camera: 5 out of 10. This is my main issue with this game. The camera is terrible. You have zero control over the camera whatsoever, and I wish they had allowed for it. As I mentioned earlier, it will sometimes cut away mid fight to show you something else that is going on, and it will frustrate you by switching back and suddenly you're getting pummeled when before you were doing good.
6. Difficulty and fun factor: 9 out of 10. This game can be quite hard. I was frustrated a few times on certain bosses, and you can end up dead pretty quick sometimes. But I would say it wasn't hard beyond the point of having fun. Eventually you get past the points that give you trouble, and you feel pretty decent about your feat. It's not the hardest game ever, but there should be plenty of challenge to go around.
I will conclude this review to say why Castlevania doesn't lose its identity here. The game feels like more of a throwback to older games in the series, namely the first castlevania and the second in particular, Simon's quest. I remember playing these games when I was a kid and it felt like I was playing a darker game, that was kind of scary in some ways. This game does that too.
Personally, it feels like a Castlevania game to me, and that's what it should do. Just because the art style is different from the others doesn't mean it can't create the same effect. It actually feels darker and more eerie with a more realistic art direction.
And the transition from 2D to 3D I think is a smooth one. Let's face it: 2D games are dying. Sure the occasional good 2D platformer shows up every now and then. But in order for Castlevania to survive it needs to evolve, adapt, and move on. It has done that here.