I have played your demo. I will apologize for having made my criticism before playing the demo because I
didn't even know it existed. I would have said something before also because, as you can see on the first page, I was awaiting for this game. For many reasons I couldn't follow the thread so, again, apologies for not having seen the demo links.
Now I'm ready to deliver a properly informed opinion.
First of all: Playing the game, FEELING it, softened my impression that it was too slow. However the impression still remains. As I said above, my favorite Vania is Adventure Rebirth. Your game has a lot of things in it that take me back to Rebirth (one of which being the maneuverable jump, THANK you for this), but the speed makes it feel a lot slower than it appears to have been designed to be. It's a strange feeling because I can obviously tell it was designed around Simon's capabilities, but it does still feel a bit too slow even for a classicvania, which takes me to the next point: Attacking feels unsatisfying and, risking repeating myself, too slow.
Simon takes a loooong time to whip forward after you pressed the button, and this slowly becomes a bigger issue as the game progresses, culminating on the first boss fight. At first you are OK and the enemies do not pose a challenge that Simon cannot overcome, but soon I realized that, were he to attack just some frames faster, he would not have to deal with the slog that is the first boss. I'll be honest with you: I cheesed the hell out of this boss because dodging the flies and lining them up for an attack so I could be free to attack the boss itself after was extending the fight way beyond my patience would let me take it. So I just made it so (via cheesing that I'm not sharing publicitly because I'm not sure if you intended for it) that I could hit the boss AND the flies at the same time, and that was it.
So, bottom line: This game could be just a tiny bit faster and most issues I have with it would be solved. And I say "most" because I have another issue with the gameplay that made it much harder than it should be: Simon can't crouch. I immediately understood why Simon can stomp on some enemies, but it also meant that floating enemies coming from below HAD to line up exactly in front of you so you can score a hit (which takes luring that is not possible to perform in a tricky situation), and also meant that I couldn't tell which enemies are stompable or not.
I mean, I imagine the rule of thumb is "if you can't whip it, it's stompable". But then there were these small blob monsters floating about that I could NOT stomp and could NOT hit with the whip because they came from below, and could NOT avoid because I was gonna fall into water or spikes. Well, what is one or two more hits, anyway...
Artwork: Absolutelly gorgeous, scary and surreal. I wish I could eat it because it's that good. It looks like Simon is moving inside a painting, it's so weird and interesting. My ONE nitpick is the one frame jerk that Simon does due to a single misaligned frame during the idle animation. That's literally it.
Music: I have some favorites (Save Room and Dwelling of Doom), but I couldn't deal with Silence of Daylight for long. It sounded too noisy and slightly off-key to my ears.
Overall, I think this is a beautiful effort at doing CVII any justice. And if there is any justice in this world, this game will come out and be recognized. But the gameplay, on my opinion, is suffering. It feels too slow for hands used to Rondo or Rebirth. In fact I would wear the douche hat and say that it feels (just a bit) slower than even the original Simon's Quest.
PS: Dear god man, if this is at all possible to you, please please shorten up the "What a horrible night to have a curse" transitions.
PS2: You can skip the Game Over screen. THIS I loved with disproportional passion.