The Long Mars is the third in a series of fantasies based around the idea that alternate dimensions rally do exist.
My favourite thing about this book was the exploration taken by the character Sally Linsey about what it means to be a daughter, juxtaposed with the continuing question of what it means to be human. These almost seemed to take a greater part in the book than the fantasy/ sci-if aspect.
Having said that, it was interesting to consider how very different ours (and other worlds) could be. I particularly enjoyed the humorous exploration of what range of lifeforms might exist out there somewhere.
A good standalone read, made even better if read as part of the series.