I am afraid I have to agree with the reviewers who didn't like "London Orbital". I originally skimmed through the book in a bookshop and it didn't appeal to me. However, a friend bought a copy for me as a gift and so I ended up reading it.
Firstly, "London Orbital" says surprisingly little about the M25 itself. Anyone interested in the history of how a major motorway came to be built in the green belt surrounding London or seeking an analysis of the effect it has had on local communities in terms of transport, economics and the environment will be disappointed. Instead, Sinclair uses the general location of the M25 as an excuse to write about anything in the area which takes his fancy.
Unfortunately this includes a lot of things which are speculative or just gossip. A good example is Sinclair's account of the housing development at Enfield Island Village. For nearly 200 years the land was previously occupied by the Enfield Royal Small Arms Factory. Sinclair drops dark hints that the land the housing is built on may be contaminated with chemicals or even radioactivity from the factory. However, it appears that the only source for this information is a conversation with a local resident who once knew someone who worked in the factory. Sinclair doesn't actually seem to have done any proper research into this subject, which is disappointing.
The Island Village issue is typical of the negativity and cynicism in this book. However, I didn't find much humour, and it all gets a bit wearying after a while. I was also wearied by the writing style which consists mainly of short sentences and missing verbs. At first this is fresh and original, but soon becomes a major headache.
Negative reviews such as this one tend to be rated badly by other Amazon reviewers, but I can only report on how I found the book. To be honest, I couldn't finish it. I thought it was terrible.