People here are a tough crowd to please when it comes to authenticity. Given the age of this site, nearly everyone who's still around is an expert in the intricacies of Castlevania lore going back for decades. Now, we tend to be a mature bunch so small departures from the lore can be excused, but larger ones like Netflix seem prone to get on our nerves.
As you guys can tell I'm personally very excited about the series, despite being a (comparatively) 'old hand' around here as well, but that has as much to do with my personality as anything else--like I implied above I did do a bit of study into Caribbean slavery when I was younger, so seeing it portrayed in a setting that makes a bit of sense (the French Revolution, i.e by extension the early-modern French colonial empire) very much tickles my fancy, enough that I can overlook the departures from Castlevania canon.
I wouldn't say the overall opinion has changed that much--IIRC the first season was well received here, but folks didn't take well to the later ones, especially given some of the, er, edginess. Like I said, we're a mature crowd, but that stuff went over the line for many of us, and I recall having to cool down a few arguments over the subject. If you're seeing the same sentiments on Twitter, I'd say it probably has to do with the popularity of Rondo/Symphony. Symphony is one of those games that had an impact even outside its typical fanbase; even people who don't like Castlevania acknowledge its influence on video game aesthetic history thanks to Yamane and Kojima's work. So a larger audience would be eyeing the new adaptation with a more critical eye. Though I must add that while my personal circle of acquaintances matches your experience, the larger, general-anime-fan-audience I've seen on Twitter seems to be unabashedly enthusiastic in their reaction to the trailer.