In Harry Potter and the Deathly Hallows, Rowling demonstrates that she really has been building up to this finale across all seven books, laying down material in earlier books to be picked up here.
After a brief, happy interlude at the wedding of Bill Weasley and Fleur Delacour, Harry goes on the run with Ron and Hermione. A coup has taken place in the Ministry of Magic. A puppet minister has been installed, with Voldemort reigning behind the scenes. Mudbloods are being rounded up. Snape is the new headmaster of Hogwarts.
They spend months on the run trying to track down the horcruxes, with little success. They do manage to break into both the Ministry of Magic and Gringotts Bank. Eventually, they learn of the Deathly Hallows, three legendary objects that can conquer death. Harry becomes obsessed with them, to the despair of Ron and Hermione.
Eventually, they make their way back to Hogwarts for the climactic battle with Voldemort. They witness Voldemort killing Snape to take possession of the Elder Wand, one of the Hallows. Harry retrieves Snape’s final thoughts and views them in the Pensieve, and learns that Snape had been Dumbledore’s spy all along and had killed Dumbledore at his behest.
Harry battles Voldemort, coming to the very brink of death, but finally triumphs. Several of his allies die in the Battle of Hogwarts. An epilogue set nineteen years later, shows many of the surviving students congregating at King’s Cross station to send their own children off to Hogwarts.
I found this to be a very satisfying climax to the series, darker and weightier than the earlier books, but without the padding of The Goblet of Fire or The Order of the Phoenix. We learn a great deal more about the backstory of the series. In particular, we learn about the young, flawed Albus Dumbledore and his manipulative ways. Not only Harry, but also his brother Aberforth and Snape were pawns in Dumbledore’s plans.
Highly recommended, if you read the entire series.
(See the Wikipedia article for more details.)