Underwhelming. But the end justifies the means, eventually, as we find out what the slightly ridiculous game of one-upmanship progresses is really all about. The back of the book summed it up pretty well by saying 'a child's game is made dangerous with adult stakes' (ie. money).
Ultimately, though, if you are not a man who lived through early 70s Britain, (which I am not), much of this may go over your head.
Also, it seems the main character has some kind of mental illness, which explains his behaviour throughout and especially at the end. But since this is never really made clear, it's not really what the book is about, whereas the book might have made more sense if it had.