Replay

Jeff Winston dies of a sudden heart attack in his 40's, but is able to repeatedly relive his life up to the original point of death, making different choices and placing his life on widely varying pathways each time. He meets Pamela by chance, another "replayer", and the book transforms into a love story in the midst of all the deaths, rebirths, and altered history the characters continually create (both within their own lives and within the world at large).

The possibilities and scenarios Grimwood creates are very interesting, and the book really makes you think about how you might personally change your life if lived over. An additional twist that makes the characters not have quite as much of a blank slate or freedom with each subsequent life is the phenomenon of "the skew", which pitches them forward a little bit farther along thier lifespan from the time before (so less time to relive and different settings at the start). No spoilers, but this has major implications toward the end of the book.

Replay has an underlying melancholy that I think detracted from it as a whole and prevents it from true greatness. Related to this, the protagonists seem to be forever regretful, which is the last thing you would expect from a person who can relive their life 8+ times.

Having said this, it is a necessary work to be read by all SF/F fans. It presents original and very entertaining scenarios and is well-written with very fleshed-out characterization. You really expand your horizons for having read it.