Let's get a few things off the bat:
If viewing a possibly "toxic" relationship will make you dislike or think this manga is bad, the story isn't for you.
If moments of painful cringe and second-hand embarrassment ruin your mood, this also isn't for you.
In fact, this is not a manga for everyone. Atleast, if you are just someone looking for romance/comedy as those types of themes are very different for this piece.

Before we begin, let's address a few things that are the main talks from readers and my personal thoughts:
1. Yes, this deals with and displays bullying. Healthy and unhealthy. It is in the title. There are some people that says this isn't, but the subject matter and even the title of the manga say otherwise. That isn't necessarily a bad thing.
2. Although one can view this as a metaphorical representation of Dominant/Submissive relationship, the material usually also touches on the social aspects of what that means and seems more speaking of something else rather than trying to show D/S in a positive light. (For reference, Nana to Kaoru does this well and bluntly.)
3. There is meaning in the manga that is positive. Something important, something misunderstood by a majority of people who stomach the first ten chapters.

I will include some *SPOILER* related content later to further elaborate some points but let's get to business.

Story/9: Yes. A story about a girl bullying a boy is good.
Why? Subtly. Simply put. From dialog, representation of art, and chapters that focus on a particular theme, this is a very strange story that is definitely more than meets the eye. Now some might disagree with me and say this is purely a story that encourages and enables both bullying and toxic relationships. Sure, you are welcome to that opinion and I wont say you are wrong for having it.
I'm saying look at it from a different light.
Reader, if you have not touched this manga at all or got past the first ten chapters, I ask you to take this into consideration. That the point of this manga to differentiate purposely hateful bullying from something else. A theme of characters with obvious flaws and displaying them openly for the reader to obviously not WANT to like. Growing and becoming more from these. As well as growing from another person and learning about yourself from the interactions of another. If you don't get that or want to understand more, I have some spoiler stuff at the VERY BOTTOM of this review. However, I encourage you to go into this manga as simply this:

A story of two people, flawed, having a questionably unhealthy relationship from the start and growing healthy from it. If something happens or is said in a weird way, ask why. Sure, it might seem like looking too deep into something that seems too shallow, but the story DOES do well in letting you know that both main characters have complex backstories and pasts that are slowly looked into as a slow burn while you read. Something sympathetic, something also along the lines of "This person is in a better position than where they were before."

Art/9: Not much to say here besides the art is really good. Main focus is purely in body poses and facial expressions. Something really important, as there is both a lot of attention to detail as well as showing you emotion better than what can be said. A lot of emotions are displayed not by words but by how exactly the characters are drawn and what they are doing, and there are panels where no words are said but something is being communicated deeper through the art alone.

Character/8: Two people are your main focus for the majority of the manga and both of them having glaring problems.
Your male MC who is usually just referred to as senpai (He does have a name though later as Naoto and is called various other nicknames) and your female lead Nagatoro.
Naoto is cowardly, introverted, and seems to suffer from anxiety constantly. While Nagatoro is a sadistic, cruel, energetic joking character. You get this quite heavily from the first few chapters in full and it is shown in a way where you aren't suppose to find them acceptable. Not these traits, and not the way these two seem to interact at first.

Yet, through their seemingly torturous and toxic relationship do these two become SOOOOOOOO much more as people. The main male character is shown to be this shy person who seems to have no friends or heavy passion until speaking with Nagatoro through an extended time and having a friend group that seems to genuinely care about him as a person. (Even through the teasing.) He seems to have ambitions and goals. Mostly in social skills and art. You get to watch these develop in babysteps as he grows out of his comfort zone in both to do better.
All because of Nagatoro. So how can a girl who constantly calls you a virgin and put you on the verge of tears help you to become better and achieve the things you want out of life? I mean, the first Ten Chapters seem to display this would have the exact opposite effect. As I mentioned before, there is a complexity to the dynamic that these two have that slowly unravels as the story goes on. Even the female character who is normally only shown to be a sadistic POS seems to have other things going on in her life. Sure, most of what is presented is her being a straight up bully, but she also seems so questionably bored. Even subtle hints at times like she has no other interests. Early on, you would thing from her actions and how she talks that she would have hobbies or goals. So there is some mystery of why Nagatoro acts in the way that she does and what is going on in her life that paints out a deeper personality.
My only critique is sometimes it feels too slow, and that there is more focus on the bullying aspect than what I previously mentioned. It gives off a perspective that this really is some kind of Stockholm Syndrome bullying relationship without the depth I explained before.
Some would disagree with me completely, saying this is completely toxic and encourages unhealthy behaviors and relationships. That it is nothing more than smut.
Fine.
The whole point of this review is to maybe play the devil's advocate and look at this differently.

Enjoyment/8:
This manga treated ME through a BDSM relationship. Chapters are sometimes hard to swallow and painful only to be relieved by the next one to make up for the social torture this displays. In the further chapters, things become more... cute and therapeutic. That there was something emotionally nice and a deeper meaning behind the early sadism and I was happy I continued reading.
Try reading the first 20 or so chapters. If you can't see it from the perspective I have detailed above, I can't persuade you anymore and this probably wont be a fun read for you. Personally for me? As someone who has been bullied and in toxic relationships seeing what this manga is about? I liked it and thought it was both cute and funny.

Overall/8: **SPOILERS AHEAD**:

I wrote this review for the fact it seemed like it was getting a bad rep from a lot of people and I wanted to come in defense of it and not scare away the people that actually would like this manga and the story.
That it is a complex romance story from a weird perspective about overcoming your personal issues and traumas through unconventional means.

"How is the manga doing that? He's just being toyed with, ridiculed, and torture for someone else's sadistic pleasure! That's the only thing you could POSSIBLY take away from this!"

Let me point out a few things from the earlier chapters. In the first meeting between the two characters, two things are obvious:
1. Our male protagonist is someone who is lonely and has low self-esteem issues who is not happy with the person that he is and wishes for so much more.
2. Our female lead IMMEDIATELY picks up on this, tells him bluntly, and seems unhappy with this.
One could look at it from the obvious perspective that it is pity or she truly finds it disgusting.

Yet, she goes out of her way to see him almost on a daily basis and, through her own ways, helps him with these problems of his through strange ways. That work.

Again, you can completely disagree and I both welcome/respect that, but I highly recommend looking more at this manga than what it is at the surface level.