Being a pretty busy person, and usually hating to read travel guides, I find that the DK Eyewitness Guides are the only ones I can stand reading - in fact, I find them enjoyable.
Their main force is that you don't have to imagine whether a destination would be something for you - the guide shows you what to expect, where others just tell you about it. That is the series' main force: They are very easily digestible.
That said, an Eyewitness Guide can't stand alone, so my wife usually acquires a Lonely Planet guide for the place, and I read the Eyewitness Guide, and the two complement each other nicely.
At 630 pages, this is the largest Eyewitness guide I have seen to date, but it also covers a very large subject: All of California, including large and comprehensive sections on both San Francisco and Los Angeles.
In addition the introduction, Survival Guide and Travellers' Needs sections that are found in every Eyewitness guide, this book consists of four main sections, roughly equal in size: Los Angeles, San Francisco, Southern California and Northern California.
The section on Los Angeles is the largest, and at 129 pages is in itself as much as some of Dorling Kindersley's city guides. The section on San Francisco isn't much smaller, but lots of pages are still left for the rest of California. In essence, you get two complete city guides and a nice country guide in one reasonably priced package.
Although I'm satisfied with my purchase, some things could be better: Disneyland gets disappointingly dull treatment, considering that it is LA's main attraction - although 4 pages are used we don't even get an overview drawing of the park, although that's something I'd really expected from the Eyewitness guide.
In more general terms, these guide are always very neutral in tone, so it's often difficult to get a feel for an attraction - it might be interesting, but is it worth the money? Is it expensive? The guide doesn't say...
As a conclusion, the book gives good value for money and is an excellent preparatory tool, although its shortcomings as a travel companion becomes too evident with use - for actual day-to-day planning, we had to turn to Lonely Planet for detailed information and subjective recommendations.