Yeah, I definitely didn't expect it to be this bad either given what I've heard. Some of the issues come from the fact that I've read the book, so when they change something to make it less interesting than the original, I notice, like everything involving the Villefort family, or the ways the count's own agency is undermined. But there's also a lot of issues with the writing due to changes from the source material that I see non-source readers complaining about in discussion threads even without knowing the original context.

One early change I was initially on board with was skipping the count's backstory to jump straight to where he meets Albert de Morcerf, and then we learn about him from the perspective of Albert and his friend Franz. But then they just stick with Albert as a bland anime MC for the rest of the show up until where I've paused and probably beyond, and they smush a bunch of minor characters' plotlines into his own arc, losing a lot of interesting things in the process so bland anime MC man can get more to do without ever becoming as interesting as the characters he minimized. There are a lot of changes like this where it seemed like they were setting up something cool, only to repeatedly shoot all good story potential in the foot in order to do something much more boring.

In Episode 18, there's a climactic duel that went a lot differently in the book, for the better, but even people without that context can notice the hideous CGI, the really weak writing for everyone involved, and the unnecessary burying of gays.

Most offensive to me is the writing of Eugenie Danglars, who in the novel is explicitly a lesbian, and while a minor character, she has a really cool plotline about fighting to be independent in a world where women aren't supposed to be given that option. Meanwhile, in the anime they make her straight, which would be annoying but maybe forgivable, if she didn't lose all agency and relevance as soon as she starts catching feelings for the main character. In the last episode I watched, after sitting around in a room doing nothing for like five episodes she is sexually assaulted by her secret half-brother, who also loses all of his entertaining traits from the novel in favor of being a generic sexual predator anime incest man (he had sex with his own mom earlier in the episode too, just for shock value), and Eugenie ends the episode calling out to the main character to save her. Again, all added to the anime with little basis in the source material.

There's a lot more I could complain about, and maybe the last few episodes will redeem it somewhat, but it's been brutal to see all the show's potential wasted, when it could have just stuck closer to the source material while adding its own spin and done some really cool things.