Okay, so I'm at the music box stage, Chapter 10, and feel like I've played enough to give it a rough estimate.
There are two stories, depending on who you believe and what interview you read them in, as to how the initial design of the game came about: Either Mercury Steam and Konami started the game with the full intention of making it a castlevania, and were merely being coy by not originally identifying it as such when the first trailer debuted, or Mercury Steam set out to make a Castlevania, but weren't entirely sure they would get the greenlight from the powers that be on it, so they made the initial design generic enough it could stand as its own property if the studio got cold feet.
The way the early stages of the game play and feel, I'm inclined to believe the latter scenario. The first four chapters of the game notably lack a Castlevania feel. Some of the environs are too bright and mystical, the enemies, with few exceptions, are largely harry mammalian creatures-werewolves, wargs, and trolls, and the supporting cast are fantastic and seem regrettably superflous to the larger narrative.
Even the combat in these early levels feels different from what, mercifully, comes later on. The titan battles and the Malphas battle particularly use an annoying reliance on the quick time event to make it through. Later battles, though still requiring the QTE to finish the boss, don't use the technique as a requirement to simply engage the enemy.
Once the game hits chapter 5, however, it really feels like the point they got clearance to make the game a 'Vania. The backgrounds are suitably dark and detailed, the obligatory castle levels the best looking and designed of the 3D entries in the franchise, and the enemies start appearing more and more familiar, albeit with their own dark twists. The tedium of the original levels quickly wears off, and the perseverance of the player starts paying off in spades.
Forgiving the first four mediocre chapters, I think the game's easily one of the best in the franchise. Again, this is my consideration up to chapter 10, so we'll have to see how the last three chapters play out, but the middle five are easily the best 3D iteration of the series we've seen so far, and this is from that rare Castlefan that actually enjoyed Curse of Darkness. . .a lot.
Sure, there are other gripes, the music is forgettable, the replay value-the desire to go back and replay through previous levels, is so far pretty slim, and Patrick Stewart's voiceplay sounds like he's reading the phone book with several warm brandies in him, but overall, I'd have to say I'm sold so far. Let's hope the next one has less fantasy elements in it.