The only thing this shares with the TV series of the same name is the concept of everyone in the world simultaneously blacking out for two minutes, during which they have a “flashforward” of their future. In the TV series that is 6 months hence; in the book it is more than 20 years hence, so the implications are very different.
It’s a fantastic concept and it’s explored in a variety of interesting ways, but it is really badly written (how has Sawyer won literary prizes?).
Although it is primarily sci fi (set at CERN), there is a murder investigation to widen its appeal, and a poor pastiche of Arthur C Clarke's 2001.
After the flashforward, people pool their sightings on a website to see if they match (e.g. if I was lunching with John, was he lunching with me?). Some find their visions reaffirming and others want to fight against their apparent destiny - echoes of Oedipus and Scrooge. Meanwhile, investigation is under way as to what caused it, amidst recriminations regarding those who died, e.g. when vehicles crashed and surgeons passed out.
Would you want a flashforward? What are the political implications for governments; insurance implications; would patent offices be swamped; would it weaken or strengthen religious belief; how would small children cope with what they see as an adult 20 years hence; could you marry someone if you knew that you would be with someone else in 20 years time? And of course the big one: is our future immutable or do we live in a multiverse?
One oddity is that most of it is set last year (2009), which was the near future when it was written in 1999, so there is unintended entertainment from the things he got wrong, though I do live in hope of newspapers voluntarily dropping horoscopes because "printing such nonsense was at odds with their fundamental purpose of disseminating truth".
Despite the high ideas, this book has weaknesses common to poor sci fi: teaching readers the science with dialogue between experts who would already know whatever it is along with trivial references to life in the future which irritate rather than illuminate or amuse (Ikea's Billy bookcase will still be around in 2009, but George Lucas still won't have filmed all of Star Wars). And there is plenty of other plodding prose, "As headquarters of numerous international organisations, Geneva attracted people from all over the world." Wow (not). There are also odd holes in the plot; for instance we are meant to believe that CERN has no emergency procedures, even of the kind that an ordinary office has?
So, read it for the concept, try to let the poor writing wash over you, and pay attention when Sanduleak is first explained.