I wouldn't say it is terrible, but I'm sure there are much better books out there--in fact I've just ordered a different one. In general, I like the "Dummies" series. Although I don't care to be labeled a "dummy", sometimes you don't want to be buried in the details and fancy tricks, you just want a quick guide to getting the simple things done, and this series is very good for that sort of thing.
But by the end of the third chapter, all the author did was rehash some mind-numbing details about what is in the program, there was nary a fun project or step-by-step problem solving lesson provided. I finally accomplished a few of the things I was interested in by skipping ahead to the sections that had relevant content, but I was astonished that it didn't cover even those superficial issues very well. So I wound up using the program's native help screens, and I have to say those were far more useful than this book.
All the while, the author uses the trademark snide remarks of this series (I'm sure the series editor requires this through some sort of template or author's guide for how these books are supposed to work). When I'm learning what I need to learn, I don't care. But when I'm not, these unfunny remarks become insufferable.
So my advice is, buy one of the better rated books in the Photoshop area.