This, my friends, is the best Touhou anime you've never seen!

But alright, jokes aside, this anime is more beautiful than I expected. No amount of trailers will give it enough justice in that regard.
I love the thick lines, so it's very much up my alley. The animation is simply outstanding. A lot of interesting decisions, for example, sometimes it goes first-person for extra immersion. You get used to CGI very fast, it's done so well that it never stands out in a bad way. This anime has fantastic, original effects, beautiful intermissions, really creepy demon designs and characters that look unique.
There is blood and gore, which is good. Limbs fly around quite often and blood sprays even more so. Characters don't mind though, they just brush it off without as much as a scream and keep fighting. Oh well... that's just how the genre works.
Some things, however, are censored. Which is weird. Because sometimes censorship is there and sometimes it isn't. I just don't know how they decided what warrants it. That said, when it's there, it's still rather stylish.
So, visually, this anime is absolutely amazing, one of the best I've ever seen, no doubt.

The composer is Yuki Kajiura, so... to no one's surprise, the soundtrack will give you goosebumps because of how breathtakingly atmospheric it is. Nothing else to add here. A masterpiece.

The episodes are a little empty. It's like nothing has happened yet, and it already ended. And that ending is often abrupt, with no cliffhanger or a defined ending scene. I would honestly go crazy if I was watching it as an ongoing instead of binging.
Besides, at this point I'm so used to great anime that don't waste time on typical "previously on..." scenes that just the fact that they were present in Kimetsu no Yaiba was disheartening. I was just sitting there thinking "why did you just waste two and a half minutes of screen time?"

Now, to the juicy part, story and dialogues.

Oh boy...
They were so poor, I'm not sure words I want to use to describe them would be approved on this site.
And I really can't explain how infuriatingly dumb they are without going into spoilers, but let's just say I can rant about them for hours and it will get heated, because I hate them THAT much.
I'll give you one example. One dialogue without context, so it's not much of a spoiler, but if you don't want even that much, just skip it.

There is a lot of exposition and not of a fun variety, just stupid. Explanations like "this sword is made of special metal", "this clothing is made of special cloth", "this mask is protected by special charms" - this all sounds like a kindergartner wrote the story.

And there are just too many instances like this. Writing in this anime is offensively stupid. In fact, here are some more spoilers for you, if you'd like more examples:

Humor... well... let's just say, it's the same as the rest of the writing. Stupid. And if in the first few episodes it looks kinda cute, later it just becomes annoying. At one point I just started skipping their comedic routine to get back to the main story, because I understood that if I struggled through one more scene like that I just wouldn't be able to finish this anime. It's really that bad.

The characters are one-dimensional and don't go beyond one personality quirk.
Tanjiro, the protagonist, is weirdly enough the best of the bunch. He is not your typical shonen hero. He doesn't scream, doesn't rush and he's very kind. But it's not a stupid type of kindness that stands between him and his mission. It doesn't look phony at all, but instead creates some of the most emotional moments in the series. I also love the way he talks to kids. He manages to make child characters way less annoying than they usually are.
Nezuko... exists. And that makes internet happy. I mean, it makes me happy too, but doesn't make her a good character at all. She has about zero development, even though she's undeniably cute. Also, please, put something soft inside her box! I just don't want to think how much it hurts with all the running, jumping, spinning, swimming that Tanjiro does.
The antagonist is... described by one of the characters the best - he is a coward. And a rather pathetic one at that. Which makes watching him a really dull experience.
Shinobu is nice. I need way more battles with her. I want to know if there are any to be expected from season 2, because this could be the deciding factor in whether I'll watch it or not. She's just that cool. Again, not particularly well developed, but cool nonetheless.
And then Zenitsu happened. And... I'll be honest, I almost dropped this anime the moment he opened his mouth. His level of annoyance is at the level of the worst One-Piece characters. And I'm saying this as a person who actually enjoys One-Piece. Stupid, loud, whiny comedic relief.
Sure, he has his moments. In fact, I'll go as far as to say his moments are some the most epic in this anime. But they are way too few to tolerate him all the other time. Which is a shame because he was the character I was most looking forward to the moment I saw his design.
Finally, while I mostly found Inosuke annoying, I just have to give props to his voice actor. He was so good with all the screaming I couldn't believe when I saw his name. The most protagonist voice you've ever heard - Yoshitsugu Matsuoka - the same guy who voiced protagonists of Sword Art Online and Danmachi among other things.. Like... holy hell... I'm impressed, I would've never guessed it was him. Bravo! I think I found my new favorite male voice actor.

Pros:

• Art and animation, especially in combat
• A fantastic soundtrack
• Loli in a basket... or a box... or a blanket...

Cons:

• Story, dialogues, characters, humor... basically everything that was written.
• A horrible ending. As if it was just an episode ending, instead of an ending for a season. You get no satisfaction at all from it.

In the end, Kimetsu no Yaiba is an empty show in a gorgeous wrapper. Because of that wrapper and the main idea behind the show, I managed to watch it to the end (of the first season). But at some point it became such a painful experience, because of the whole stupidity of dialogues and story, that I couldn't recommend it to anyone else in good faith.
The writer's skill was so poor that it didn't just become an average show with some plot holes and tropes you can forgive. It actively worked against everything this show was doing right. You can see that she (writer) had amazing ideas, but lacked the talent to put them together. These ideas - points A, B, C in the story - are marvelous. But the path between them is simply atrocious. Sometimes you're watching a moment of unmatched beauty, both visually and emotionally, and are thinking - there it is, fantastic, gorgeous, breathtaking! And everything in that moment of silent visual storytelling is clear without words... but then the moment keeps dragging, they add words: start talking about exposition, backstory, put a completely unnecessary comment from the heroes. And all you can do is sit there and think: "No, please, stop, not now, it was so perfect"... But alas, the moment is gone.
And this is what killed Kimetsu no Yaiba for me. And I'm just upset that such a potential was ruined. Be it lack of talent or just lack of experience - it doesn't matter.
The writing quality killed this anime.