I myself find CotM to be somewhat hard at times, but all the difficulty in the world won't stop gameplay from degrading into bland sessions of scrolling through levels that have a gothic theme. They've got the prettiness down (as far as 2D art goes - I say the way it's put together in most instances is purely awful, what the hell happened to having real staircases?) and the music as well, but the gameplay just isn't there.
You'd think that in this day and age they'd figure out how to make it a challenge for the reflexes and not simply memorizing stuff, rather like I hear Maximo (Ghosts to Glory/Zin, take your pick) has accomplished. Instead, they shift the emphasis from memorization to level grind/getting the crap kicked out of you when you dare go too far into the game too quickly, inventory management, and even so a hint of memorization persists if you wish to use it (you don't have to, though). AAARGH.
On with my first comment that deviated from the flow of my comments, about 2D art. SotN's flat-art stuff is good (mostly) and classically inspired, but the folks who assembled it have an aesthetic sense that would make any self-respecting dog (that happens to eat poop every now and then) cringe. We have lots of uninspired ledges and bullshit elevators to ride about on, and the "omg cool factor" wore off the first time I encountered them. I didn't find any room to be particularly interesting the first time I entered them, and I have no real desire to see them again. The same holds true for Circle of the Moon, and while I've logged many hours into that one I'm always looking for a [boss] fight or to doublejump up to an unsuspecting skeleton to send his bones flying before I hit the ground...'cuz that's fun.
Staircases were cool. In SotN we have a bunch of strange flat rooms with even stranger arbitrary blocks here and there [hanging in midair] for the player to hop about on. One of the most fascinating things about the original Castlevania was that while your character couldn't heave himself up blocks by the arms, he could walk up stairs...WALK...not needing to exert himself unnecessarily in jumping through warehouses in some inglorious cratefest. Hitting medusa heads when you were in the middle of a flight of stairs? Badass. Super CV 4/Rondo made it much easier for us, letting Simon moonwalk and drop off a flight of stairs and letting Richter jump on and off stairs at will, by magic! [No, it's not magic. That's the whole point. It feels like you're actually a part of something big, grand, epic.]
[bit of a red herring/diversion here]
The realism introduced by the stairs seems unremarkable now, but at the time it was a selling point. Hey, Mario runs through these crazy looking levels, but Simon Belmont is in a CASTLE, and people understand that world on a level you can't with a Mario game -- while Mario games are lots of fun, Castlevania (as it was supposed to be) puts you in a fantasy setting where the laws of physics still hold sway, and you can't do really crazy stuff all the time. Simon has to be really careful to win his game, and it's a more heroic challenge to undertake (so it appears, anyways). Super CV IV and later games did indeed mess with the formula of realism a bit, but all in the name of better gameplay.
[back on track]
Now here's something to consider -- Super CV 4 used sprite rotation on Simon's arms so you could hit things in eight directions. That made the world more interesting with enemies on platforms above and below you. In SotN, what are we back to? Braining undead apes with tapir bones, that's what. I know there's a lot of stuff added with "l337 w1kk1d k3wl m0v3z," magic, and odd/useless subweapons but at the end of the day, neither I or a rat can give a damn (much less an ass) about button sequences. Learning intricate button sequences isn't a part of gaming for me, because it has nothing to do with entertainment or life whatsoever. I don't expect Konami to release a full-body motion sensing suit for use in their games, but using the button press combination approach is lame [using the attack combination approach, though, is great by me - take a look at the combat system in the newest Zelda, nice stuff considering it's much less complicated!]. I also feel the same way about games that add on all sorts of buttons when the main game can be done well enough by four and maybe two shoulder buttons.
I know some folks like that sort of game, but I really don't see what's so appealing about it. Combos just don't equal entertainment for me...I like games that give you a set of rules and present you with a large number of possible scenarios you have to deal with. I know some will scoff, but that's one of the things I think has kept Counter-Strike alive all these years, and kept it alive for me. A CV game obviously is at a disadvantage in that the other players aren't humans...but with a bit of good programming and a wide variety of moves (as opposed to a wide variety of dumb enemies onscreen) you can solve that and the human tendency to find shortcuts/unfair advantages (infinite combos/"CPS1 chains" and AWP horez) all at once.
[If the designers were really interested in entertaining us, they'd do something with that bad old RPG system or that silly two-button gameplay mechanic (with Fighting Street combos added on -- in this day and age that represents another ancient and frankly obsolete way of forcing the player to make sacrifices in the name of entertainment, instead of looking for better control devices and schemes), right?]
That's just how I feel. If you really like the game, hey, I don't want to turn you off from it. I know I can't speak too much about the game's intricate details as I haven't played the whole way through (not even close), but some things about the game (mechanics, design philosophy and the like) won't change.