I've bought a few of the Rough Guides film-oriented series of books, and for the most part I've enjoyed them. However, speaking generally about the series I've noticed that within the books there's frustratingly little direct reference to sources, and the comments on individual films or on groups of films seem to rely more on generally-held and widely-repeated claims than on innovative research, and hence I would say that these books should really be seen as an introduction to the genres they cover, as opposed to a detailed analysis of these genres.
On the subject of this specific entry into the series, film fans who are already familiar with the literature produced about films noirs will find this particular book frustrating, as for the most part it simply repeats generally-held comments about the movies that have been explored in greater depth elsewhere: there's little originality in terms of research or critical insight into the movies. More pernickity noir-addicts, like myself, will find the book's use of the incorrect (but now moderately widely-used) plural 'film noirs' to be mildly frustrating. (For the uninitiated, 'films noirs' is considered more 'correct', as it obeys the rules of French grammar and 'film noir' is, after all, a French term.)
Likewise, despite its attempts at serious criticism this book is not a good source for students of film who are studying at anything above 'A' Level: the entries on individual films are very short and don't go into enough detail, and furthermore there's a lack of referencing of sources, so the book doesn't leave a strong enough 'paper trail' for an undergraduate student who may be preparing an essay on the film noir genre (or 'style', if you prefer).
However, casual fans of these movies may find the book helps them to identify other movies that they may like to watch. For casual fans of films noirs, I would recommend this book, and I would also recommend Silver and Ursini's FILM NOIR: AN ENCYCLOPEDIC REFERENCE TO THE AMERICAN STYLE.
This book gives a very good account of American film noir, ranging from black and white classics such as Double Indemnity to more recent films such as Body Heat, The Last Seduction and The Grifters. Unfortunately the book is let down by a lack of attention to countries other than the USA. There is one 28-page chapter entitled `The Dark Side of the Earth' which purports to cover everything outside the USA, but that chapter is notable for some bizarre and inexplicable omissions. From Argentina, the book includes Fabian Bielinsky's 2005 film `El Aura' but does not mention his earlier classic `Nueve Reinas'. There is no mention of the Chilean classic `Los Debutantes' which features a marvellous portrayal of a `femme fatale' by Antonella Rios. The only Spanish film mentioned is Almodovar's `Carne Tremula'; there is no mention of Aranda's classic `Amantes' which features an excellent performance by Victoria Abril, nor of the same director's historical film noir `Carmen' which features a memorable performance by Paz Vega in the title role. (Ironically, the book does include the American noir `Carmen Jones' which is based on the same Bizet original.) The five pages on France include the classics `Rififi' and `A Bout De Souffle' but does not mention `One Deadly Summer' which features a memorable performance by Isabelle Adjani. Personally I would give this book four stars for its coverage of the USA, but only one star for its eccentric and appallingly incomplete coverage of the rest of the world.