Yes, the infrequent releases and the short chapters are frustrating - but otherwise, this manga is just about perfect.
I see a lot of complaints about the most recent arc dragging on, being repetitive, and so on. I can understand that viewpoint, but I really don't agree. Ren has such a traumatic past that he has lived in a false persona for years, refusing to allow his true self any say. Even before taking on the character of 'Ren Tsuruga' he was unhappy and troubled. If the mangaka had been the type that would have resolved all that easily, she would not be anywhere near as good as she is.
The characters are real, and funny, quirky, likable.
The story and plot may seem slow, but I personally think that is partly because the manga is so addictive - when you go back and read the volumes again, what took so long when reading each chapter as it came out (think the dark moon arc) actually doesn't take that long to get through.
The art is fine to me - it improves drastically as the years pass. What the the manga lacks in beautiful art, it gains in characterization.