None of these are "Low Rated" because it's pretty hard to find a drama with really bad ratings. However, they're in the 7-low 9 zone.
I'd call them "unpopular" because you don't see them hyped that often, or are criticized often.
Cheese in a Trap, I've heard a few nasty comments about the main leads appearance as well as how he was really manipulative.
Playful Kiss, this is either a loved classic to some people, or the most disgusting, manipulative drama out there. Haha, I guess I like manipulative ml's...
Memories of the Alhambra, people really seemed to hate the plot holes, Park Shin Hye, and the ending. I watched it because the author of W wrote this one. It was pretty good, it had a descent plot.