This is the part where we get a few dozen (or hundred or however many) pages into a book and tell you how badly it sucks. Or how great it is, I suppose. No, probably how bad it sucks.
Truth told, this one doesn't actually suck... It just strains credibility to the breaking point and beyond. Kind of like Stirling did in his Draka series. That time, pretty much everything that could go wrong for the good guys actually did go wrong and the result was that the most racist, brutal society imaginable ended up ruling the world.
Dies the Fire takes us in the opposite direction by putting good people in a bad place but letting pretty much every turn of luck go their way. If they need something (or someone), it (or he) just seems to magically appear.
I'm not giving you much in the way of plot points but suffice it to say that this is sort of an apocalyptic what-if kind of thriller. Personally, if you're into this sort of thing, I would suggest John Birmingham's After America instead. Better written and more believable. Both require a certain suspension of disbelief (all science fiction-type writing does), but Birmingham only asks for it once at the beginning of things... Stirling demands it on pretty much every page.