When I started reading this book, I was rather surprised not to find any film version of the story. There is plenty of action with the smuggling of secret plans, followed by a large scale aerial attack on the USA. If the book had continued in this vein, with initial setbacks but eventual victory over the aggression (and perhaps the setting up of a better world order as in Wells' other books) then it would definitely have been material for the cinema, especially with monorails, that epitome of modernity, everywhere. However, the war doesn't go that way, instead we hear about the struggles of the hero, Bert Smallways (who has been mostly a spectator in the first part of the book), in a post-apocalyptic world. Since we've had plenty of exposure to this sort of idea nowadays it felt a bit of a letdown.
However, the book does give a fascinating portrayal of an 'alternative history', and of Wells' worries about the future. He foresaw the likelyhood of 'total war' and the importance of air superiority in future conflicts. One feels that he rather overdid the collapse of society - we're somewhat used to the idea following a nuclear war, but his explosives weren't that much more powerful than those available when the book was written in 1908. Overall I would say that it is definitely worth reading if you are interested in the changing ideas of progress and conflict, but not for the story itself.