I'm reading one right now that is written quite well, but I do find it starting to meander - I'm interested in seeing how she's going to wrap it up and make the necessary connections.
There was one memoir that I read that wasn't terribly well written and I remember rating it quite low ...it was Robert Goolrick's The End of the World as we Know It.
I found I went on a terrible rant when rating and discussing the book - "the book itself" was not well-written and I found Goolrick to provide a run on raging complaint and rant - at times romanticizing, at others raging against his parents and childhood. In this case, I really did not like this memoir at all, not against his life in any way, but I think the book itself could have used a much stronger editor to guide and shape his rage into a more readable memoir. (Sorry if I babbled here.)