I picked this up because it had the "controversial" tag here yet wasn't loli, shota, rape, or senseless violence... After looking at some spoiler tags, I realized this sounded AWESOME. It sounded like the reasons it pissed everyone off were all things I'd LOVE. And, uh... I did.
This isn't the perfect manga. As a romance, it's not impressive. But as a comedy, I found it hysterical, and it kept me hooked from beginning to end just to see what madness would implode next. I adore the femc -- the girl in the boy's body -- because she's so goddamn DIFFERENT from shoujo protagonists (and, heck, shounen deuteragonists, josei protagonists...) that I'm used to. She's repulsive, unhygienic, rude, selfish, cruel... she's horrible, it's great.
I think there's definitely a trans narrative hidden in here that someone could dig out with the right credentials. Two people that find themselves more and more comfortable in the body of the opposite sex? This was not written to be a trans story, but I think it has something going for it. MC's struggles with his double-internalized homophobia also aren't as ridiculous as you'd expect from a gag manga.
What's interesting is that most gender benders have the wacky hijinks ensue from characters having to Act Like The Opposite Gender, which is silly and weird, because girls aren't used to misbehaving like boys! (etc), but in this one... they already were. Femc was already brash, violent, and dirty; MC was already dainty, quiet, and kind. Femc, given the body of a man, was able to flourish -- she found herself loving girls, goofing off, flirting, working out, doing whatever she wanted. MC, however, was straddled with the terror of being A Girl: periods, men making unwanted advances, societal expectations, men making unwanted advances, the conflicting desire to respect the body of the girl he loved and also to explore it given the opportunity, men...
Of course, this implies the concept that girls can't be gross and boys can't be delicate, but as a product of its time and place, I think it's amusing in its own right. It's a comedy, not a thesis.
My one gripe with the manga (putting aside the romance, which, in Senbongi's case, gets really creepy) is how it playfully toys with gender roles while also remaining remarkably (sigh) heteronormative. Femc does not, under any circumstances, want to return to her normal body, because she now has a girlfriend that she loves and fears losing. Despite a few poignant dokis around her female body, her girlfriend also isn't too into the idea of dating a girl (even though she literally is). Senbongi supposedly loves his best friend, but only if he has Girl Holes. It's really weird. I guess it's a straight people thing. Love doesn't overcome gender boundaries in this story about zany gender antics. Don't go in expecting BLGL or heartwarming romance. Love is very conditional for these people. It reminded me a bit of Ayakashi Triangle, the way the casts approach this "we're the same gender therefore No" dichotomy of, uh, "love". These manga would have gone entirely differently if the authors believed in lesbians.
One thing I think a lot of reviews fail to consider is that yes, the main romance doesn't work out, and that's a... good thing? MC would have been miserable with femc. She literally only had eyes for her girlfriend and didn't give a flying FUCK how he felt. If the manga rushed and contorted around enough to make that happen, it'd feel even more cheating than what people are mad about. Like... did you expect femc to just change her entire personality and disposition and fall in love with a dude after she's shown so much interest in women? MC also became more and more painfully aware of how much she didn't like him no matter what he did, so flipping that around and having them suddenly hook up would just be bizarre. It'd be a disservice to the characters she spent so long creating at that point.
The gags? They're fun. The art? It's nice. And some weirdos aside, the characters are endearing -- at least if you, like me, enjoy obnoxious assholes. I dunno, I feel like this is only controversial because people went in expecting the same shit they get from every shoujo manga ever and instead got something subversive.