Philosophy of science can be fun at times. This book proves it. Feyerabend wanted to shock the scientific community when he wrote it, and was very good at it.
What are the main theses of the book? First, "the" scientific method does not exist. Scientists have to invent new methodologies on their way to discovery. Second, sometimes progress requires theories that contradict facts as scientists perceive them. Third, sometimes it requires irrational arguments in order to get your point across in science. Fourth, science does not deserve a special status in a social debate.
To many scientists, these ideas would sound provocative even expressed in the politest of manners. But that was not Feyerabend's style. On the contrary, Feyerabend overdid many of his statements ("The only principle that does not inhibit progress is: anything goes"), and he made rude remarks. Some of his statements are not very well supported by arguments. That, of course, is hardly surprising for someone who defends some irrationality in science. But it will not convince a hard-boiled rationalist. Also, Feyerabend's exaggerations made it easier for his critics to criticize him.
And still, Feyerabend knew what he was talking about. Scientists are indeed sloppier and more irrational than they pretend to be. Galilei's statement that the earth rotates around its axis did contradict the "fact" that nobody ever noticed any influence of this rotation. And it was not science that first pointed out the dangers of environmental pollution.
Conclusion: Against Method is a classic, and it deserves it. It's a very interesting book for those who know how to read it.