Harry Potter and the Deathly Hallows
Fred sums up Percy pretty well when he calls him a "Ministry-loving, family-disowning, power-hungry moron" (30.171). Yep, Percy has definitely been that guy for the past couple of Harry Potter books.
But Percy redeems himself in the end by showing up at Hogwarts and fighting against the Death Eaters alongside his family. He even jinxes at the Minister of Magic, Pius Thicknesse (and cracks a joke in the process). We definitely like this new Percy a lot better than the stuffy, uptight, self-righteous Percy of the past.