Well, I nearly didn't buy this book because of the previous review, and I'm glad I changed my mind. First off, the previous reviewer is quite right that it is far away from the classic Wyndhams both in terms of subject matter and quality of writing - so please don't expect it to be terrific because if you do, you will be disappointed.
But it is a perfectly OK sort of read - a Boys from Brazil/Archangel type thing (tho writing standards not up to Harris!). It has suited me perfectly for a couple of evenings while not wanting any sort of challenge. And if you are at all a Wyndham aficionado you may well be interested at the points where the style is recognisably him. The main problem of the book is, I think, correctly identified in the introduction - the hero/narrator lacks the clear voice that is so characteristic of Wyndham's better novels and without that one is not brought into the action and over the weak bits of plotting. One stands outside judging the book far more than in any of the others. It may well be right that part of this problem is created by Wyndham's decision to make Johnny Farthing a cultural misfit - in that he ahs lived many places and sounds wrong in all of them. I suspect that part is also about the difficulty for the author of identfying with him in circumstances where (without entirely giving away the plot) he doesnt physically stand out very distinctly - Trollope always said he wrote with a picture of his heroes and heriones always clear in his mind.
Anyway, I would say it is worth a read just out of interest if you ever really liked John Wyndham - just don't expect too much ...