I loved this book. I appreciate hard science fiction, even though I'm not a scientist and can't tell if the science is ridiculous or not.
I liked the para universe section the best. However, I understood the differences between the Rationals, Emotionals and the Parentals the first three times it was described in the story. I didn't really need it described another 5 times.
Asimov has an incredible imagination. I recommend this book.