I just got back from the fifth movie. It was ok, but they cut out way to many details. If you haven't read the book, you won't know why a lot of what's going on is going on.

For example, you wouldn't understand why three people are caught trying to use Umbridge's fire, but then there are 6 people in her office in trouble for it. Or pretty much anything about the prophesy.

And before anyone says "The movie is made for people who read the book," I disagree (or think that if they did that, it's a stupid reason). Most people who read the books think the movies are disappointing (or at least, that's what everyone I've talked to says).