I'll tell you my thoughts but before that, let's break some 'misconceptions' about shonen itself.

Shonen definition:

A manga in shonen demographic is made to appeal for young children of 9-17 years of age with moral values about "overcoming all despair and living life to the fullest".

But this definition has been lost in the sauce as more shounen mangas kept coming out over the years and the magazine's editors had to make the stories set themselves apart from one another to sell more copies to a wider range of audience so they allowed the authors to add a more mature tone to their stories while retaining the common moral of the shonen spirit in order to expand their popularity.
If demon slayer came out in the 80's, almost all of these "otakus" will call it an "underrated masterpiece". But now what's really happening most of the time is grown ass men hating on children because they like simple shonen stories and not some life changing mangas with heavily depressing themes.

I'm never telling you to stop hating but at least understand the story yourself and formulate your own opinions or just purely hate because it brings a personal joy in your leisure time.

that's the hating game that i like to see because i like hating too, it's very fun when it's done right. what i don't like is the ''lmao its bad', circle-jerking cowardice. Yes, this yap session was needed so you can see my review with a fresh perspective and actually think and judge for yourself if my opinion is good or bad on its own, instead of comparing something you heard about this series in the past by some people that you can't even remember their names of.

And now i'll tell you about the good things and the bad things in demon slayer:

(+) Neat artstyle and character designs:
If you only seen the anime and you're not familiar with the manga, i urge you to check out at least the volume and colored chapter covers. Its very stylistic with some sengoku period influence that flows neatly throughout the story. Don't even get me started on the character designs, i truly believe the author has done a excellent job in making the character look's resonate with their abilities and their environment. you're not really missing out a lot if you're a anime only and you've watched demon slayer seasons but for people who haven't seen the anime or can't wait for the trilogy movies to release, the DS manga absolutely hold on in its own right and you'll not be disappointed when it comes to art.

(-) Obnoxious troupes and Ambiguous powers:
The easy picks for the most annoying character award for anyone who read or watched demon slayer is zenitsu and inosuke.
zenitsu is the demon slayer version of sanji from one piece expect he's ugly and a coward. he flirts with every girl and thats the running gag. You can see why people hate him.. Inosuke is a wild dude wearing pig mask but underneath he has a good looking face.
There's variety of reasons why inosuke is hated; he keeps yelling a lot and his power can apparently rival any demon with no explanation. This same can be said about zenitsu too, when zenitsu passes out or sleeps, he can take on a alter persona where he's very serious and brave enough to oppose any demon. Now this brings us to the open to interpretation/ ambiguous powers. A lot of the power system is either poorly explained or not gone in-depth at all in the story. I'm not naming the powers here because that would be spoilers in the grand scheme of the story so ill try to summarize it:
Sword techniques are powers that can conjure natural elements (like flame, water etc.,) that compliments one's breathing style. Breathing styles are derived from one ultimate breathing style that has been lost, hundreds of years ago. All breathing styles have forms that can go from 1st form to any amount such as 16th form in some cases. Example: Water breathing style can create layers of sharp water waves that flows in a path that the user cuts. The user masters the a particular breathing technique while elevating his body to perfom more forms.
What is odd you may ask? as you keep reading the story, theres so many forms and so many higher ranked characters that you just cant comprehend what makes them powerful and how they even got that power in the first place. Demons are a exception because they're unexplainable in nature. But the human powers are very much left to interpretation too. There are detailed ranks in demon slayer corps (a secret militant force) but it's very much open to interpretation on which characters are powerful which ones are not so powerful in the high ranks. This might be a spoiler, but remember i talked about zenitsu? somewhere in the story, he opens his eyes while in his alter persona and stays the same way throughout a fight. So what does that mean for all the times he acted as a dick? we may never know. Its for you to figure it out because i dont even know either. Maybe you can slap a sticker and call it character development if you want.

(+) Dead people actually stay dead:
We did it guys! we actually found a shounen jump manga where the dead doesn’t come back with ass pulls! Yes, seriously. Every character who dies has a reasonable and satisfactory end with enough care to their emotions and the bonds they shared with others. You might be thinking if a good human character dies and got brought back as demon, that will count, right? Yes, it does but there's not 1 character, good or bad comes back again in the main storyline. Because the story is about slaying the demons, equivalent to undeads or vampires in a more clear term; the story mainly focuses on the emotional struggles the characters go through and finding salvation rather than bringing them back in a flashy way to only suffer and fight to death again (urm.. that one manga called sorcery fight). The author actually respects their characters and gives them enough time to do everything they want to do in the story which is a rare occurance in shonen standards if you're not aware of other popular mangas in the magazine.

(-) Tiring plot structure:
Heres how the story arcs flow:

new demon appears --> demon slayers fight --> death or disability --> (insert a sob story flashback and monologue on how the character had gone out of their house for a while and some demon took that chance to kill their family) --> demon slayers win but at what cost? --> main villain gets one step closer --> rinse and repeat.

this is how almost all the arcs are structured and this is why some people hate demon slayer and call it bad. its not that the story itself is bad, its just structured in a way that's so predictable and forced for most people.
is the hate actually valid? its up to you to watch/read and decide. for me, there's a lot of emotional and beautiful moments that are worth overlooking the tiring aspects.

(+) Emotionally kidney touching moments:
Demon slayer explores the strong psychological desire to love and be loved in all creatures.

There's a hindu proverb that goes something like:

No child is born inherently evil.

The story emphasizes it and gives you a character's life story which answers on how a normal person, got twisted, broken and became a murderer. It's a very powerful and sensitive topic but demon slayer handles it so well like a folklore and not "you are just like me, adolf h!tler. you can change" kind of sentiment that most shonen mangas take.
I'll never tell much about the plot lines or scenes because that would ruin your curiosity. I'll only tell you the good and bad things. It's for you to process it and see if this story is worth your time.

Here's my list of favourite characters:
Tanjiro "the yapping fighter" kamado and his sister, Tanjiro's master, Tanjiro's angry and devoted swordsmith, Zenitsu "the thunderclap freak", Inosuke the extroverted boar man, , Burning-will Rengoku, Gyutaro the big brother, Cool guy Uzui, Genya the american eagle, Sanemi the crazy one, Yorichii "the honored one", Kokushibo "the six eyes", Mitsuri and Iguro "the made for each other couples", Kind hearted warrior Gyomei, Giyu "the silent night" tomioka Akaza "the self-called hater of weak yet ironically, the protector of weak", Tamaya "the hope", her loyal assistant Yushiro and their cat chachamaru.

conclusion:
With all that said i think, this manga was not that fun but it was perfectly emotional when it need to be and it was absolutely a good read. I didnt talk about tanjiro and nezuko or how nezuko being alive against all odds. I'll tell you why its not a plot hole; it's because she must be alive for the plot to even kick in, to begin with. Otherwise, it would be stupid to follow through all of this emotional adventure for them to die and fall short before the real fight even begins.
i reccomend you to watch the anime but if you so desire, you can start reading the manga too and you'll find something to love and appreciate.