When I first read this manga as a wee-child, this seemed the height of emotional and sexual mannerpunk, but upon rereading, Motoni Modoru's characters reveal themselves to be, well, Motoni Modoru characters. Jeanne of Aestheticism.com once wrote an insightful look into the kind of modern melodrama that Koi ga Yurusu Hani represents, but suffice to say, the crux of the plot revolves around the way the main characters Yamazaki and Fujio have twisted themselves into knots trying to justify their feelings for each other in spite of and because of their reluctance to sleep with each other. When their girlfriends (Reiko and Miku respectively) finally goad them into a sexual relationship, the thing comes to a head, in part because the characters keep arguing over whose feelings have been "raped" the most. Fujio and Yamazaki are less fully realized human beings than walking examples of overwrought ~feelings~. I have never once been able to follow Fujio's chain of thought, and it took meeting Imagase from "The Cornered Mouse…" before I was able to properly appreciate Yamazaki.
Miku and Reiko fare slightly better as real human beings, though it's telling that because we see more of Miku, she also engages in the same emotional gymnastics that Fujio and Yamazaki do, whereas Reiko comes off as more "real" simply because we never have to scratch her cool, uncaring exterior. Equally telling is what happens to Katsumi, Miku's boyfriend on the side, who is introduced as an anchor but then rapidly becomes a deus ex machina for Motoni. He spends most of the latter chapters shouting at various characters and thus explaining the story to the reader, and without Katsumi, I have a feeling most of the last arc of the manga would be inexplicable.
So, in the end, Koi ga Yurusu is more Tori Maia than Miyamoto Kano. A better comparison might be Nitta Youka's "When a Man Loves a Man" series, though directly comparing the two, I think, shows off Nitta's more even-handed, subtle approach to her characters. It's a fascinating enough melodrama, if you're into that kind of thing. If you're asking me, my final verdict is that all the characters would be too exhausting to be friends with in real life, the kind of people you'd always be texting, "for the love of god, go home, you're drunk."
Koi ga Bokura wo Yurusu Hani