Reversing course from the previous game, the Wide Open Sandbox approach is back and in a big way. The centerpiece of this game is an elaborate recreation of Hogwarts in which you can pretty much go anywhere at any time with nary a loading screen in your way. As such, the gameplay is heavy on running around the castle and performing tasks for various characters, particularly students whom you want to recruit into Dumbledore's Army. However, any part of the original story that took place outside of Hogwarts is skimmed over quickly, including the whole sequence in the Department of Mysteries, which you'd think would have had a lot of gameplay potential.
After Ron and Hermione were Promoted to Playable in the two previous entries, this game reverts to just Harry being the Player Character, with the exception of brief episodes in which you play as the Weasley twins, Sirius Black, and Dumbledore.
Building on having gotten Ralph Fiennes last time, there are now twenty-one of the film actors voicing their characters for the game, including Rupert Grint, Tom Felton, Matthew Lewis, Bonnie Wright, Evanna Lynch, Katie Leung, Warwick Davis, Natalia Tena, and once again, Ralph Fiennes.
- And Now for Someone Completely Different: This game allows you to briefly control Fred and George, Sirius Black, and even Dumbledore! The DS version has Lupin also playable during the Department of Mysteries battle.
- Big Brother Is Watching: One of the portraits that provides a shortcut is hesitating to give it to Harry, because directly across from him is a portrait with literally a giant watching eyeball looking around. It takes Harry causing a spell to get a curtain to cover the eyeball portrait for him to get the password.
- Final Boss: Voldemort, with you playing as Dumbledore.
- Foregone Victory: In the Dumbledore vs. Voldemort duel, Dumbledore is unaffected by any curses which hit him. The duel can only end with Voldemort's defeat.
- Hopeless Boss Fight: When the Room of Requirement is discovered, Harry has to fight the entire Inquisitorial Squad. The fight is unwinnable — you will lose (if not, run out of time) and Harry will be brought to Dumbledore's Office as per the plot.
- Implausible Deniability: When the trio are looking for talking stone gargoyles to help Dean Thomas to get him to the DA meeting they come across one in which they ask him if he talks but it replies no repeatedly.
- It's Up to You: As is so often the case in these games, Ron and Hermione seem to expect Harry to do all the work. This time, Hermione's recurrent excuse is that she and Ron are prefects now and shouldn't really be breaking rules.
- Rewarding Vandalism: Inverted for once, with this game rewarding you for tidying up Hogwarts instead. Oddly, this is the one game that actually justifies the trope, as there's a whole section of the game where you go around vandalizing the school in defiance of Umbridge's takeover. And yes, you can still get points from tidying up Hogwarts while you're wrecking everything for Umbridge.
- Secret Society Group Picture: Discussed trope. When Colin gets asked to join the other DA members in the Room or Requirement, he asks if he should bring his camera there with him. But then he immediately changes his mind, lampshading that he probably should not because it is supposed to be a secret. Coming from Colon, this is a rare form of intelligence.
- Video Game Cruelty Potential: You can hex random students in the hallways. Most will just run away, but some fight back. Fred and George even encourage you to practice your curses on "any passing Slytherin", though you can curse kids from other houses as well. You can curse teachers, but they'll just put you in detention.
- You ALL Look Familiar:
- When you go to find the first years who had skipped detention with McGonagall, they're also the same age as the Trio.
- There's a random Ravenclaw with Seamus' face, just with different hair. It is highly creepy when you see them in the same shot.
- "You!" Exclamation: Filch does this when he catches Fred and George transforming a school corridor into a swamp.