It really should have been an hentai as some previous posters have said. Why? Well, put it this way, it would have made for a better manga overall, better sex scenes for instance, that and well the abrupt end wouldent have been so bad.
Storywise it's not half bad, but it's not great either. Art is great, on par with many a hentais out there. It easily surpasses most of the crap thats released today. No complaints there.
What is lacking is the story, and the consistency of the plot. It really leaves us with as many answers in the end as in the beginning, not much progress at all is made, and yeah the ending is rushed unfortunately.
Better sex scenes, better consistency overall and a better ending, and this manga would have been a whole lot better. So yeah, turning this into a hentai and keeping the plot would have made for some damned good hentai, thats for sure.
6/10
Edit*
It's gender bender big time, so beware if you dislike that genre!