I just finished Her Fearful Symmetry by Audrey Niffenegger, and can rate it no more than 3/5.
Now, don't get me wrong, I can suspend belief with the most credulous of humans, and have an enormous amount of fun whilst doing so, but the Final Solution, the Coup de Grace [sorry I don't know how do do the mark over the "a"] of the story was just sooooo unbelievable, amateurish even that it put me off.
Niffenegger's characterizations were so well done, her portrayal of OCD was to my eyes completely on target that it's just a shame that in the final analysis the story simply didn't hold water. If a sequel is in the works, and the ending begs it, I don't know that I'd bother to read it.