I personally am going to wait for the general consensus of reviews before buying. Even though the demo by itself seemed good enough, who's to say that the main game won't be bad?
If some of these complaints are true, then they should have focused more on making a good linear game that took some new ideas and executed them in a good way than have a big, open-world that is full of problems. It seems like linear 3D Castlevania games always seem to review better than the ones that try to be like Metroid. As great as a 3D Metroidvania would be, I'd take a more linear Castlevania over a flawed Metroidvania game any day. (for the 3D entries)
Of course, the above is my inference of 3Dvania from what I have observed. We will have to wait until the game releases to get all of the review scores...