The following contains massive spoilers for Ready Player One, both the new movie and the novel it is based on. Only read this if you have seen the movie.
Ready Player One is a story filled with so many pop culture references that getting them all on the big screen was always doing to be essentially impossible. As such, it was a foregone conclusion that the Ready Player One movie was going to need to make some changes to the source material. While the movie was largely able to do that without losing the spirit and fun of the book, the version of the story we got on screen was a very different beast.
This is not an exhaustive list of every difference between the book and movie, as such a thing would require an immense list of mostly insignificant details. Instead, this is a list of the big changes that have the biggest impact on the overall story, likely with numerous little changes referenced throughout as we get into the details. Let's dig in.
Wade lives in Columbus, Ohio. The city of Columbus, Ohio is the home of most of the live-action portions of Ready Player One in both the book and the film. However, in the novel, Wade actually grows up in The Stacks outside of Oklahoma City. He's just as poor. His aunt is as unsympathetic in the book as her boyfriend is in both the book and movie. Eventually, after becoming a world famous Gunter, he earns enough money to move, and so he packs his meager belongings and takes a bus to Columbus. Since that's where Gregarious Simulation Systems (called Gregarious Games, an earlier company title from the book ) is located, it's a sort of Gunter Mecca. Most of Wade's time in the book is spent living alone in a small one-room apartment in Columbus.
The copper key is won in a race. When the movie opens the location of the copper key has already been located by some other Gunter, but in order to obtain it, you have to win a race with some pretty impressive obstacles. In the novel, Parzival deduces where to find the key himself, locating a detailed recreation of the Tomb of Horrors, a location from a classic Dungeons and Dragons module, on the planet Ludus, where he attends high school inside the OASIS. Upon reaching the end of the tomb, he must face a demilich in a best two out of three matches game of the arcade game Joust. Upon winning the key, Parzival discovers that Art3mis has also discovered the tomb on her own, though she'd lost the game of Joust and so had been returning to try again.
The gates simply reveal the clue to the next key. Once one of our hero characters obtains a key in the movie, they use it to unlock the gate to get the clue to the next key. However, in the book, there's a lot more to it. Each key yields a clue to the gate location, which is found elsewhere. Then, once the gate is found, another challenge must be overcome to complete it and get the clue to the next key. In the case of the copper gate, Parzival completes it by playing the role of Matthew Broderick in a perfect recreation of the 1980s classic WarGames, where he's required to recite every line of dialogue and perform every action just as it was done in the original movie. We do enter a movie in Steven Spielberg's adaptation, but it isn't WarGames.
Parzival gets the quarter from Halliday's Archive. The film depicts James Halliday's archive of notes as a physical location inside the OASIS, but in the novel, it's an actual physical collection of journal entries that the creator of the OASIS published on the event of his death. While the journal, Anorak's Almanac, as it is called in the book, does yield the very first clue of the Hunt, it's less important as a plot device in the book than it is in the movie. It's also important because here is where Parzival is awarded the quarter that allows him to eventually win the Hunt. In the book, Parzival is chasing a lead on the Jade Key that, while it turns out to be a dead end, results in him being awarded the quarter for playing a perfect game of Pac-Man. In the movie, Parzival basically forgets about the quarter and never thinks about it. In the book, he knows the object is valuable, but he's unable to ascertain its use until it happens.
I-r0k is Sorrento's hired gun. One of the characters with a greatly increased role in the film as compared to the novel is the avatar known as I-r0k. In the film, he's a fixer of sorts used by Nolan Sorrento to do IOI's dirty work. He's the one who eventually uncovers Parzival's real name, leading to the destruction of his aunt's trailer. In the book, I-r0k is a teenage Gunter like the rest of our main characters, though not one that commands much respect. He does eventually lead to IOI learning who Wade is, but through much more indirect means, and only after trying to blackmail Parzival and Aech into telling him where the copper key is located. Once that fails and I-r0K makes good on his threat, he disappears from the book.
The characters meet each other in real life early on. Following the explosion at the stacks, Wade is grabbed by somebody who turns out to be working with Art3mis, real name Samantha, who is part of an organization that is fighting against IOI's attempts to take over the OASIS. This organization is an original creation of the film. Samantha lives with her grandparents in Vancouver Canada in the novel. This change puts the two characters together much earlier in real life than it happens in the book. In the novel, Samantha and Wade don't meet in person until literally the last couple pages of the book, though Wade does see a picture of the real Samantha earlier. Likewise, Wade meets the real Aech when the pair meet up as part of the preparation for the final battle, making the revelation of Aech's true self come much later. Interestingly, Wade never actually sees Shoto (the name for Sho's character in the novel) in person. They have a personal conversation where Wade learns Shoto's real name, Akihide, at one point in the story, but when Wade arrives at the place where Akihide and the rest of our heroes are, the Gunter has decided he doesn't want the distraction of meeting in person before the final battle, and the two don't cross paths in person before the novel ends.
The High Five work together. From the moment in which Art3mis thinks she knows where the Jade Key can be found, we see the High Five, the top five people on the scoreboard, working together. Daito and Sho seemingly come in from nowhere. In the book, following the Stacks explosion, there is a meeting between the five where Parzival warns them of what happened to his aunt, but any hint of working together is basically shot down by every other person in the meeting. Daito and Shoto work together, but the other three work solo. Which leads to Ar3mis finding the Jade Key on her own, followed by Aech, then Parzival.
The Jade Key is inside The Shining. Art3mis is the one who gets the idea to look for the Jade Key inside the movie that James Halliday once watched with a woman he loved. This sees all five of our heroes enter a fantastic recreation of the Overlook Hotel where they do in fact find the key. In the book, the riddle that leads to the Jade Key is totally different. It references the classic text adventure game Zork, leading the Gunters to play the complete game on a planet that recreates it in graphical detail. The Jade Key, in turn, leads to Parzival to take Blade Runner's Voight-Kampff test to open the Jade Gate, where he plays a first-person version of classic arcade game Black Tiger.
The Jade Key leads to Castle Anorak. After Samantha and Wade get separated we learn that IOI has already deciphered the Jade Key's riddle and they have barricaded themselves inside Castle Anorak, the OASIS home of James Halliday's avatar. While that does happen in the book, it's the Crystal Gate, not the key, that IOI closes off from the rest of the OASIS inside the castle. The Jade Key riddle actually leads IOI, but with Parzival not too far behind them, to the planet Syrinx, a planet built to pay homage to the album 2112 by Rush. There, Parzival gets the Crystal Key, and almost as soon as he does, IOI uses the Orb of Osuvox to keep the third gate secure.
Art3mis ends up working for IOI. IOI raids the location where Wade and Samantha are hiding and Art3mis ends up caught in the net. She's forced to work for IOI's oology division which hunts for the egg. In the end, this is a benefit, as it gives our heroes somebody on the inside to take down the shield. In the novel, Wade ends up getting himself intentionally picked up by IOI as part of a larger plan to infiltrate the organization to gain information on them and take down the shield. He does this without the knowledge of anybody and is able to successfully do what he needs to do and then escape, all before anybody realizes he was there.
Daito takes on Mechagodzilla with a Gundam. In addition to these two massive robots, there is a third large robot that features in the big finale, the Iron Giant, piloted by Aech, but it's Daito's appearance in the Gundam that turns the tide. The book's final battle has many more giant robots in it, as completing the Jade Gate rewards the player with a giant robot of their choice. This is where Sorrento gets Mechagodzilla. Several other IOI employees who are sent through the gate get robots of their own, including all five Voltron lions. Aech is the one who actually pilots a Gundam in the book. Art3mis takes control of Minerva X, Shoto controls Raideen, and Parzival pilots Leopardon.
Daito survives the story. When Daito makes it to the final battle in the movie, his avatar makes it much further than it did in the novel. When Toshiro Yoshiaki, the man behind the avatar, makes it to the end of the movie, he makes it a lot farther than the original character did. Following the discovery of the location of the Jade Key, a massive battle ensues between Gunters and IOI as everybody tries to obtain their own key. In the battle, Daito is apparently killed, but later we learn that not only was the avatar killed, IOI actually sent people to Toshiro's house to kill him, and make it look like suicide, in order to take him out of the competition. Shoto eventually passes on Daito's most powerful in-game item, a beta capsule that transformed him into Japanese hero Ultraman, to Parzival, which he eventually uses against Sorrento in the final battle in order to take down Mechagodzilla.
Parzival opens the Crystal Gate himself. In the film, the Sixers set off the Cataclyst as soon as Parzival and Shoto reach the final challenge. However, in the book, the entire sequence is quite different. As previously mentioned, Parzival et al. already have the Crystal Key when they enter the castle, but his team knows something IOI was never able to figure out, you need three copies of the key to open the final gate. Art3mis, Aech, and Parzival do this (Shoto's avatar died keeping Mechagodzilla busy) but before they can step through the gate, the bomb goes off. Only Parzival's extra life keeps him in the game. The Crystal Gate challenge includes playing a high scoring game on the Atari arcade game Tempest as well as performing the entirety of Monty Python and the Holy Grail. However, the two challenges do end in the same place, locating the Warren Robinette easter egg inside of Adventure.
The final battle takes place in the back of a truck. Most of the end of Ready Player One takes place while Wade and the rest of the High Five are inside the OASIS, but also on the run from IOI, this means that, while Aech is driving the van, Parzival is in the back trying to play video games. It makes for an added element of action, but it's one that doesn't exist in the book. There, the remaining four members of Parzival, Art3mis, Aech, and Shoto, are approached by Ogden Morrow inside the OASIS as they are planning the final attack. He offers to fly them all to his home where they can mount the attack in safety. It turns out he's known more about Halliday's contest than he ever let on, and while he won't help them win, he will keep the spirit of the contest alive by making sure there are no external problems that could prevent the right person from winning.