Sawyer's continuing presence on award shortlists is a mystery to me. His Hominids is possibly the worst book ever to win the Hugo (and yes, I have read They'd Rather Be Right); and The Terminal Experiment, while not quite as dire, is certainly one of the least impressive Nebula winners.
So when I say that Rollback is the best book I have read by Sawyer, this should be understood as damning with faint praise. The prose somehow seems a bit less clunky: the tedious undergraduate-level discussions of philosophy and science are wisely constrained to the first half of the book; the two story lines - the central character's unexpected rejuvenation, and the decoding of an alien message - come close to reinforcing each other.
Yet in the end, it doesn't work. The biggest flaw is that while our central character is undergoing the dramatic changes of rejuvenation, and the consequent disruption of his life with his wife and family, we get very little sense of being inside his head. The second huge plot problem is that the alien messages come only once every 18.8 years (well, actually every 37.6 years): surely once contact has been established, one would set up continuous transmission in both directions, even knowing that there would be an 18.8 year lag?
Having said that, it's a mediocre book rather than a bad one. Probably going last on my list (certainly below "No Award"); but I haven't read Scalzi yet!