Stirling's first trilogy on "the Change", starting with "Dies the Fire" was excellent. and if you haven't read it, start there first as this book will give away a lot of things from the first trilogy.
If you have read the first trilogy, I strongly recommend this one. It is set 20 years after the Change (so 12 years after "a Meeting at Corvallis") and delivers excellent action/adventure plus interesting ideas on how things would continue to develop, post-Change. Stirling has a great ability to sketch out plausible settings and characters while still keeping the action moving along. His battle scenes are top rate and remind me of Bernard Cornwell.
The book centres around Rudi Mackenzie, who was a realistic 8 year old in the last 2 books of the first trilogy (avoiding the over-sentimental approach to children that many authors suffer from) and now he is a confident young man, very plausibly drawn as the charismatic not-quite-heir to the "Clan Mackenzie". Naturally there's evil for Rudi to fight, and he's forced to travel away from Oregon to do it - giving Stirling the chance to show us more of post-Change America, and I for one relished the journey with him.
And we have some hints about what caused the Change, which I'm hoping will be filled out in later books.
His writing is powerful and not for everyone, as you can see from the negative reviews of some of the books in the first trilogy, but if you enjoyed it, don't be put off by the negative review of this one (which frankly I think is mischievous - if you detest the first 3 books, as that reviewer plainly did, why would you bother to read this one ?) this is well up to the same high standard and with lots of interesting new developments.
Stirling's ability to describe the Change and developments afterwards remind me of Max Brooks outstanding World War Z, and it had the same effect of getting inside my head, so I'd find myself thinking about what I'd do if it actually happened...
I have already read the next in the series (Scourge of God) and am now waiting impatiently for the finale (Sword of the Lady) to be published in the autumn of this year !