As I ranted recently in another thread on this topic, the Birnbaum quality has gone down considerably in recent years. They obviously have a set number of pages (256?) and as things are added to the parks, they just cut down on how much they write about older attractions. Thus the Carosel of Progress hasn't been listed in several years, nor was Timekeeper, for instance. And the details on the rides were trimmed as other features were added.
In addition, particularly since 9/11 as Disney has changed things rather rapidly, Birnbaum has taken to describing things in the past perfect tense : This restaurant HAS FEATURED prime rib and chicken, etc., instead of this restaurant features prime rib and chicken. It's like they are too lazy to check. I realize Disney has been changing things more rapidly in recent years, but the use of vague terms to describe things makes it appear they haven't been to the park lately.
As for the Unofficial Guide, it is much more comprehensive, but is darn sure that it's going to say something bad about every single attraction and hotel and restaurant in the place. I suppose this is to cover themselves, but it gives the book a negative tone.
And yes, I know Disney is not perfect and is not what it used to be. But the negative things included about everything gives the book a negative tone.