Shishunki Bitter Change is both a rare gem and an unoriginal flop at the same time.

What is rare is to find a genuine body swap genderbender drama that doesn't ruin itself with stupid comedy. As any fan of serious genderbender can most probably sympathize, the number of genderbender stories that are not either

a) ecchi fan service, or
b) ridiculous comedy,

...is exceptionally low.

In addition to this, the characters are quite well developed. It's a character-driven drama, and its characters are its main strength. There are a few tropes, to be sure, but they are not executed too blandly. The relationship aspects are also handled well, in my opinion. Another very unique and wonderful trait of this manga is how much time it covers. Most body swap stories are short-term events. Shishunki Bitter Change covers a total of 8 years, through elementary, junior, and senior high school. This time span adds to the realism and really helps to articulate the characters and how they change over time.

The reason it's an unoriginal flop is a little hard to say without spoilers. But let's just say this:

How do most body swap stories end? If you like that, you'll probably be satisfied. If you don't, you may feel horribly let down by the end of this manga. And that feeling of disappointment is amplified several fold due to the same time span and realism that is the manga's greatest strength. That said, after re-reading the ending myself, it is more ambiguous than I gave it credit for. Perhaps the author felt torn between going one way or the other. Either that, or whoever translated it intentionally used ambiguous language.