This was one of two guide books I relied on for a recent trip to Bangkok (the other is the Moon Guide for Bangkok, also recommended). I have always found Rough Guides to be most useful and a cut above Lonely planet, Frommers and the also-rans. This book for Bangkok did not disappoint.
The details provided by this RG served me well. I had been to Bangkok before and the RG helped me find new, more esoteric sites I had not seen on prior trips.
The book, like most RGs, "tells it like it is" and will recommend NOT going to some sites. For example, RGs tells the reader that one of the Death Railroad museums (for an excursion from Bangkok) is essentially terrible and a waste of time. The same museum is described by Frommers as (paraphrasing) "only for the most dedicated war buff." Which description do you trust? Well for "research" I went to the museum in question and Frommers lost all credibility with me.
Overall, this compact, yet detailed, book was one of the two most used books on my trip. This edition is up to date and even does a decent job of explaining Thai history.