At the end of every year at Hogwarts, Harry often found himself in some sort of conflict. Sometimes he was forced to face off with one of Voldemort's supporters, while other times he came face-to-face with Voldemort himself. This would result in some kind of epic battle, in which Harry would have to demonstrate his skill and bravery to come out victorious (or even just alive).
While the final battles of each year were all important to the overall plot of the Harry Potter series, there were great differences between these scenes in the books compared to their film adaptations. Sometimes the movies had to cut out extensive dialogue to keep the films from being too long. Other times, film creators chose to add more dramatics and flair to keep audiences in suspense. No matter the reason for the changes from book to film, a look at their comparisons might give audiences a better perspective of each of Harry's victories.
Sorcerer's Stone
In both the book and film, Harry came face to face with Voldemort in his first year at Hogwarts. He and his friends got past obstacles that were meant to protect the sorcerer's stone, and Harry's selflessness resulted in him getting exactly what he wanted: the stone, but not for his use.
The Sorcerer's Stone movie is very close to its source material. Harry's battle with Quirrell and Voldemort went largely the same, but the obstacles guarding the stone were slightly different. In addition to the flying keys that Harry had to catch, and the giant chess game that allowed Ron's skills to shine, Hermione had her own moment in a potion-related puzzle that had been set up by Snape. While this small scene may have seemed insignificant and low in drama to the film creators, it did help to show that each of the golden trio had their own strengths that helped them reach the stone.
Chamber Of Secrets
In both the book and movie, Lucius Malfoy plants Riddle's diary on Ginny, knowing that it would lead to the Chamber of Secrets being opened. During the final battle, Harry goes into the depths of the chamber, meets Tom Riddle, defeats the basilisk, and saves the day.
In the book, Harry does considerably less running around. The movie added a suspenseful sequence in which Harry runs through the pipes and tricks the blinded basilisk to allow himself to escape back to the main chamber. This added scene meant that there wasn't enough time in the film for Dumbledore to explain Lucius's motivation for planting the diary: he had hoped that Ginny opening the chamber would have incriminated Arthur Weasley, putting an end to the anti-dark magic legislature that Arthur was pushing through the Ministry.
Prisoner Of Azkaban
In both the book and the movie, Harry has a confrontation with Sirius Black, only to learn that his godfather had not been responsible for his parent's death, but that Ron's rat had been. Sirius and Lupin reveal Scabbers to be Peter Pettigrew, but all evidence is lost when Lupin turns into a werewolf, and Harry eventually has to free Sirius using time travel and the fan-favorite spell in Harry Potter, expecto patronum.
The action between the Prisoner of Azkaban book and the movie is largely the same, but once again, what the film was missing was the important explanations that the book provided. Harry learns in the Shrieking Shack that James, Sirius, Lupin, and Pettigrew had been The Marauders that had created his map, and that they had turned themselves into unregistered animagi.
Goblet Of Fire
Harry's battle at the end of Goblet of Fire was the first time that he faced off against Voldemort at full power. He used Harry's blood to resurrect (a mistake that would ultimately cost Voldemort victory). Despite his fear, Harry chooses to stand and fight as opposed to hiding. To both Voldemort's and Harry's surprise, their wands connect, and Voldemort's recent kills are ejected from his wand, creating enough of a distraction for Harry to get back to the port key.
In the book, more takes place before Harry faces off against Voldemort. For example, Voldemort tries to use the imperious curse on Harry but is unsuccessful. In addition, Priori Incantantum, which is the connection that is seen between the dueling wizard's wands, is different in the Harry Potter movies than it was in the book. In Goblet of Fire, Harry and Voldemort's wands connect because of their common core. This unintentionally replicated the spell that wizards can use to see the recent spells a wand has cast. This was a phenomenon that took even Dumbledore by surprise. In the movies, however, it is often shown as the byproduct of the spells of any two dueling wizards colliding.
Order Of The Phoenix
The final battle in Order of the Phoenix takes place at the Ministry of Magic as Harry and his friends try to fight off Death Eaters. In both the book and movie, Harry is lured there, having been led to believe that Sirius was being tortured. A battle ensues and Sirius is killed.
When Voldemort shows up, he and Dumbledore battle, and in both print and on the screen, audiences get to see the two masterful wizards duel at full strength. The difference between the book and the movie lies in Voldemort's possession of Harry. In the book, Voldemort causes Harry so much pain, that Harry begins to beg Dumbledore to kill him. He does not try to fight Voldemort out or tell him that he feels sorry for him. He only wants the pain to end, and wishes to join Sirius in death. Voldemort had never experienced love and had therefore never suffered a loss in the way Harry just had. The pain of Harry's grief was so strong that he had no choice but to withdraw from his mind.
Half-Blood Prince
When Harry and Dumbledore go to the cave in the Half-Blood Prince book, they encounter the same obstacles that are seen in the movie. Dumbledore drinks the potion which severely weakens him, they retrieve the fake locket, fight past the inferi, and return to Hogwarts.
In the book, once the two have arrived at the top of the astronomy tower, Dumbledore instructs Harry to put on his invisibility cloak and go get Snape. Just as Harry becomes fully concealed, however, Draco burst through the door to the tower and Dumbledore quickly petrifies Harry before he is disarmed. Harry then stands, frozen and invisible, as Dumbledore is killed. There is a certain impact to this, over Harry being hidden below. Dumbledore had used his last moment before being disarmed by Malfoy to petrify Harry, instead of blocking Malfoys spell. Dumbledore had intended to be killed by Snape with the Elder Wand never having been won by another, ensuring that Voldemort could never get ahold of it; a plan that was foiled in his attempt to protect Harry.
Deathly Hallows
Perhaps the most criticized change in the Harry Potter movies was the final battle between Harry Potter and Lord Voldemort. In the movie, the battle takes up the entirety of the castle. The two fly over the grounds, tangled together as they try to apparate. Eventually, they both tumble into the courtyard, where they take up their wands for one last attack.
The scene in the book is considerably calmer. Harry and Voldemort circle each other in the Great Hall, watched closely by the fighters of both sides. Harry tells Voldemort that he cannot win. He explains that the Eldar Wand had never been Snape's and that he had earned the wand's power by disarming Malfoy. But Voldemort still chooses to attack. Unlike in the movie, when the Elder Wand's spell rebounds on him, Voldemort does not disintegrate away. Instead, he falls to the ground, showing that he had only ever been a man.