Super premise, and realised with some expertise, but I didn't like it that much. It struck me as over-controlled.
It seems to me that all Adam Roberts' books are about how people generate a pocket universe around themselves, in which they live oblivious to the pocket universes of others. Events seem to have an obvious meaning within your pocket, only to be wrenchingly different for other people, even people very close to you. Love between people does offer some sort of bridge between these lonely universes, but is fraught with misunderstanding. Sometimes I felt that because he wanted to stick to his philosophical premise, Roberts was holding himself in too tight, not trusting himself to let the story loose, so it wasn't ever quite as much fun as it might have been. It was ironic and sarcastic in place of playfulness.
There has been some criticism of the fact that the romantic interest - an american scientologist - is both several decades younger than the hero-writer and a lot more overweight. Her physical appearance is described several times as both frankly fat and as beautiful. I personally did not find this fat-phobic or offensive, but I know others have felt differently.