I am only about 50 pages into Charles Yu's How to Live Safely in a Science Fiction Universe, and already I love it so much. It involves time travel, but it is not literally about time travel, the way my favorite science fiction novels are not about the future as much as they are about humanity.
I recommend it, but only for some people. If you're a huge sci-fi novel fan, this actually may not be the novel for you, as it's much more introspective and much less plot-driven than the most popular sci-fi novels. Read the Publishers Weekly pan on the Amazon detail page. It will turn off most people, and some of you will find it intriguing. Those are the ones who should probably buy it.
[Related: Almost none of my favorite books have a 5-star average review on Amazon. In fact, most books I've picked up with an average of 5-star reviews on Amazon are disappointing, especially if reviewed in heavy volume. My theory: anything sufficiently bold and interesting will cause some readers discomfort, and anything that's reviewed so universally positively by so many people is probably either too bland to be of interest to me or too partisan to merit reviews from those with opposing viewpoints.]