I do not share the negative reviews that have been written about this book. In my opinion, this is a very good sequel to the "Moat in God's eye".
Indeed, I believe that - hoping not to offer too many spoilers! - the choices made by the authors are logical and not at all less worthy of the plot exposed in the original book.
For example, since the civilisation on Mote 1 was going to "fail" in a very short time after the humans left that planet in the 1st book, it would not be very likely that a not-so-far-away in the future comeback by the humans on that planetary system would find the "earthlings" (sorry, the "motelings") back "on speed" once again. And, the very fact that there had already been countless cycles - along with other findings of the 1st human expedition - suggested that the "asteroidal" civilisation around Mote 1 must have had a non-negligible role, particularly during the "low sides" of the Mote-1 cycles.
Once that path has been choosen, I think that the next one (who was going to be the main human character) was only logical - and also very interesting!
I did not feel that the 1st part of the book was particulary slow or boring. However, I do agree that, starting from the "big moment", the pace does quicken quite a bit.
All in all a very entertaining read - sometimes even risking to be an intellectually (what-if) stimulating one.