Americans Hate Tingle: Nanako's rude personality and actions were despised by many American fans. In Japan, not so much.
Darkness-Induced Audience Apathy: According to some reviews, many readers found the characters so repugnant that they just gave up reading. With the English release dropped, it's as if the publishers felt this way too.
They Wasted a Perfectly Good Plot: With Akira going through so much suffering and learning about the unpleasantness of girl life, you'd think that Nanako would be subjected to the same thing with life as a boy. The answer is a big, fat, "no", and her time in Akira's body is a marked improvement over Akira's time in his own.
Values Dissonance: The whole premise, given that the two leads are praised for conforming to their switched body's dated gender stereotyping.
The Woobie: Imagine having somebody switch bodies with you... and your friends and family are all happier with the result. Now imagine that your best friend starts lusting after you, you won't be able to get your body back for quite some time because the other switchee won't let you have it, and you have to learn all the repugnant things about the opposite sex while your body-snatcher is living it up in your body, no worse for wear and rolling in women. This is your life, Akira. God help you.