I'm not going to mince words here. This thing was terrible. It's probably among the worst manga I've ever read, and I've read a lot of manga over the years.
There were a bunch of reasons this didn't work for me, but here are the biggest ones:
The Art
So, not the biggest reason I didn't like it, but the art definitely left me disappointed. Normally I don't mind older art styles. This one looks like it came out of the late 80s, and wen I looked it up, it started in 1990, so I wasn't far off. The problem wasn't the age, though. It was that much of it felt incomplete. Eyes were often left unshaded. Hair often looks more like incomplete line work than something that should come out of a person's head. In fact, much of the art looks like incomplete line work. All of this makes the art look messy and unfinished. I don't think this was a stylistic choice, however, as there are panels and pages throughout that DO look like they were finished, which leaves me wondering why so much of it looks so bad.
The Characters
They were all flat and one-dimensional. No wait, scratch that, there was ONE character who felt like a properly fleshed out manga character, and that was side-character/little brother Yuuki. He's a little jerk, but he has a REASON for being a little jerk (he's a third-grader whose room has been girlified and given to some stupid chick). He practically hero-worships his older brother
Otherwise, the characters are mary-sue/gary-stu shells. Kotoko is a stupid girl with no hobbies or aspirations, and but for a crush on Irie because he's hot and intelligent, has no motivation either. It's a good thing her crush on him is defined by his good looks and intelligence. Otherwise, she might start to hate him because he's an ass hole when she realizes he wasn't the good guy she thought he was.
Speaking of Irie-the-love-interest, he's just a hot(?), intelligent ass hole. That's... about I can say about him. He's just a jerk with a lot of brains and supposed beauty. Well, there's one more thing I can say about this gary stu. He never studies (apparently, he has a form of photographic memory that allows him to understand everything the first time he reads it), and despite never practicing or exorcising, can kick butt at tennis tournaments. And despite hating helping others and being a super-genus, he's also the best teacher in the universe. Because apparently, Tada-sensei was desperate to find reasons for us to actually LIKE Irie despite the fact he has all the personality of a rock.
Otherwise, we had one-dimensional side characters. Kotoko's female friends with names I can't be bothered to remember; "Kin-chan", a guy who is obsessed with Kotoko and marrying the girl (and I'm convinced is a stalker); Irie's mother, a woman so obsessed with getting a daughter that she dressed Irie as a girl until he was old enough to understand what was happening and later is desperately trying to get Kotoko as a daughter-in-law; and lastly, The Dads, who are practically interchangeable as they just want to convince Kotoko and Irie to get married.
Story
The story I've seen before.
Girl tries to tell guy she likes him, guy turns her down flat. Then another trope gets introduced: girl moves into guy's house for reasons. That pretty much sums it up. Yup, that's it. Well, I guess there's some stuff with Kotoko desperately trying to pass tests because her head is full of rocks and blackmailing/begging Irie for help studying. There's also a sports festival with its own tired set of cliches.
All in all, it's just not worth it. There are so many other shoujo manga that are better. This one just hasn't aged well at all.