I expected to find the science fiction part more interesting, as I've read far too many books on the physics of time travel, but it was actually the other way round. By reducing the maths content of his earlier book, Paul Nahin has made the physics of time travel bits significantly more approachable (there are some pages full of equations, but they're nowhere near as scary as they may appear at a glance). It'd probably help to have physics and maths A-levels, but it certainly doesn't require an undergraduate training. There is plenty here that I have never seen presented in such an effective way for that kind technical-end popular audience, and it's worth buying the book for that alone.
By contrast, the fiction-based parts don't work so well. This is odd, as Nahin includes as appendices two published science fiction stories he wrote in the 70s, which are both very readable, if a little stiff by modern standards. He knows how fiction works. Yet what's missing from the sections on the science fiction approach to time travel is any sense of narrative - we are overwhelmed with example after example (which require repeated checking of the footnotes) of every tiny variant in the portrayal of time travel - it's a factual overload, where a lot fewer examples with more detail and exploration of what's behind them might have worked far better.
I was also a little horrified by the grey-background end sections of each chapter, which ask the reader questions, supposedly to help them probe their understanding of what has come before, in what felt a very condescending, back to school, style. These might work for some, but I hated them.
The good news, then, is that you get two books for the price of one, and the physics of time travel one is really interesting, but as a single entity it didn't work well for me.
Review by Brian Clegg