As someone who never liked the first series and felt it was a major betrayal of expectations and promises, here are my gripes:
Hiring Warren Ellis, who is notoriously awful at writing stories about faith or religion with any semblance of nuance or respect (see: Supergod) was a fucking blunder. Muddying the waters on how faith and the power of God works in Castlevania was a massive mistake and they shot themselves in the foot by confusing it, something that Nocturne barely fixes - but in the process also screws over the internal logic of the world in the long run.
Forgetting Grant was a huge blow to the potential of the series, IMO, because without that human element of "a non-powered hero, trying to do the right thing", what we get boils down to Gothic horror superheroes versus the League of Doom (of which the "Dracula's court" plot supplied unnecessarily).
Abandoning Dracula as a recurring villain kills the spirit of the series, and the framing device of the Belmont bloodline's interactions with him from a writing perspective. Each hero is fundamentally designed, ultimately, in contrast to Dracula - and would be in a better or more faithful adaptation a driving point for each season, potentially.
People kvetching about the need for "more plot" have clearly never seen what can be done with a short series or OVA, or shounen in the vein of a "monster of the week" format (see: Stardust Crusaders, Phantom Blood, etc.). Adapting Castlevania, III especially, was a very easy task if they managed to keep the atmosphere for what it was, and embrace the simplicity of "the journey to Dracula's castle". Instead, it got lost in Ellis trying to inject Reddit-tier atheism and quips instead of properly dealing with the subject of 'faith' in a series where religion is objectively real and efficacious against monsters.
You do not have to have a long-form or deeply character-driven plot for Castlevania, necessarily - but you also have to take what you are writing and present it seriously.
Nocturne is a consequence of Netflixvania's failings, directly. Not that I'd expect anything better to come out of it, because they're obviously pandering to the audience they cultivated under the direction they went with the previous series. But the fact of the matter is that you can very clearly tell by the writing (see the clip of Richter's "I was about to say something cool but fuck it" moment) that the series is being helmed and written by people who do not get it (the vibe, the story, the feel of Castlevania), nor do they care. There is an underlying apathy, if not resentment for the content being created, because these people do not respect the "dumb video game show".
These writers are akin to those who look at the Symphony of the Night English opening, the one with the script by that hack Blaustein - and say, "WELL CASTLEVANIA IS JUST A SILLY SERIES LOL LMAO".
I wanted the show to be good. I really did. Shankar outright claimed his hatred for bad adaptations, and promised to capture the series faithfully. But it's not, and the people who are working on it evidently do not care for the original games, because they cannot be bothered to match or even write around the core premise or vibes of the original. There is a fine line between "what they need to change for an adaptation" and spurious inventions and completely missing the tone and atmosphere of a series, no matter how scant the writing is.
That being said, in the hands of competent writers, I think that a Castlevania anime (inspired heavily by Vampire Hunter D) could've been fucking great. I think that AoS would've made a perfect shounen, and actually has 'enough' story to potentially build around with the 1999 Demon Castle War, and with the thematic conflict of Soma's identity, and ESPECIALLY the theoretical fight choreography due to the Power of Dominance. I just wish that the foundation for that to happen was not written by people who are completely apathetic about making something good.