This manga will leave you saying, "Huh, that's it?" when you get to the last page. I was literally counting pages and double-checking websites to make sure that chapter 6 was, in fact, the last chapter. (It is, unfortunately.)
The characters and storylines had potential, but never really went anywhere: Sun Choi (the slutty boy that Seyun resembles)? He shows up only once and no explaination is ever provided for their relationship, despite it constantly being mentioned that Seyun takes a lot of grief for the fact that they look alike. Why would a guy like Seyun do that? The storyline involving Joonsuk's smarmy older brother? Far too easily taken care of after all that build-up it got. (And what were Joonsuk's real feelings for Seyun anyway?) Seyun's deep-seated issues with family and his resulting committment-phobia? Once again, speedily resolved (if you could even call it a resolution). Seyun's father's debts? The author didn't even bother to try on that one. And the title--"U Don't Know Me?"--I'd assumed it would have to do with Yoojin discovering Seyun's hardcore lifestyle. Nothing happens there either, despite the author really playing up Seyun's dual nature. To me, this was the biggest disappointment of all, that Yoojin remained naive about Seyun all the way through. Without this major development, how could we, as readers, honestly believe that theirs was a love that could withstand anything?
If these things all got the development they should have, the series would have tripled in length (at the very least). Since this was originally published as a doujinshi, the author wrote it knowing that it would ultimately have to be a short work, so why create so many plot complications if she knew that the majority of them would never get the chance to fully bloom? As it stands now, readers are simply left to wonder what might have been.