A Feast for Crows is not a bad book; I'd give 3.5 stars, but I round up to 4 because this one has been unfairly criticized. George R.R. Martin is still a good writer, both in the technical sense (solid prose and dialogue), and with regards to character development. Unfortunately for this book, though, it's the fourth in a series, and we readers have certain high expectations; someone coming to it without reading the previous three might not understand what everyone's complaining about, but that person wouldn't understand much of anything because these books are anything but standalone.
So the problems here are mostly editorial decisions. The biggest one is the pacing: chapters are suddenly twice as long, but very little happens in them. There are three central POV characters: Brienne, who spends the whole book wandering the riverlands (now Arya's gone somebody has to do it) looking for Sansa--a dull plot if there ever was one, as we know where Sansa is and that Brienne won't find her; Cersei, who tries to rule King's Landing but sees little action until the last chapter or two (I'd been looking forward to finally seeing into her head, but what was there disappointed); and Jaime, who is involved in several events of secondary importance, but for the most action-oriented plotline in the book, his is somewhat lacking. All of these plotlines, as well as the more minor ones, are as well-written as they can be and are placed in wonderful, three-dimensional settings, but the readership has gotten used to several huge, game-changing events per book, and that they don't provide.
Then there's the decision to include secondary plotlines, with one or two chapters per POV character. This is a bad call in my mind not only because we've seen how quickly Robert Jordan's series devolved once he began to focus on secondary characters we cared little about, but because neither the Dorne nor the Iron Islands plotline is that fascinating. In the previous three books, the offstage events added depth to the story, and I fail to see why the same technique couldn't have been used here. The kingsmoot is excellent and would have made a great prologue or epilogue, but the other Iron Islands chapters are dispensable. And it seems to me that the entire Dorne plotline could have been eliminated without any great loss, although if Martin wanted to keep it, he could easily have elevated Arianne to the status of main character and written the entire subplot from her perspective. That brings me to another point, though: Martin's portrayal of women's sexual behavior leaves something to be desired. He seems to believe that teenage girls losing their virginity on one-night stands is the norm rather than the exception, especially bizarre in a culture as obsessed with virginity as the one he's created. This stands out coming from an author whose portrayal of women is otherwise quite good, particularly for fantasy.
Ultimately, this is a decent book; it's not trash, but I don't believe that the slow pacing or even the division into two books was really necessary. Here's to hoping Martin returns to form with A Dance With Dragons!