Overall, the Sorcerer’s Stone movie takes very few liberties with the book. A few minor scenes are cut out or re-arranged, but all the biggest moments are there. At least, until they go down the trapdoor, that is. Then everything changes.
In the movie, the harp Quirrell left behind is enchanted and keeps on playing right up until the kids are about to jump through the trapdoor. In the book, on the other hand, the harp is not enchanted and Harry has to play a tune on a wooden flute that Hagrid gave him as a Christmas gift. Interestingly enough, it’s a gift from Hagrid that helps them get past the obstacle left there by Hagrid …
Devil’s Snare is also very different. Simply relaxing is not enough to save them; it’s not until Hermione lights a fire that they’re able to get away from the deadly plant. But more importantly, in the movie, this is Hermione’s big heroic moment, and she saves them singlehandedly through cool-headed thinking and her immense knowledge of magic. In the book, she has a moment like that, but it happens later, in the potions room. Here, she panics and forgets she’s a witch entirely until Ron frantically reminds her she doesn’t need wood to light a fire. Unlike her movie counterpart, she works better when she has plenty of time to think things through.
In the key room, the keys don’t attack Harry when he gets onto the broom. Instead, they’re just very fast and difficult to catch. Ron and Hermione ride brooms along with Harry, and the comparison to Quidditch is much more obvious: they work as a team, but it all comes down to Harry catching the key, which is a stand-in for the Golden Snitch. Harry’s skill at Quidditch is one of his defining features, perhaps second only to his courage and self-sacrifice, and turns out to be useful in several non-Quidditch related incidents throughout the series. Aside from the keys, he will also use his skill as a Seeker to get past a dragon and escape a room full of fiendfyre.
The chess game is more-or-less the same in both versions. I do think it’s very interesting that Harry, Ron, and Hermione take the places of a Bishop, a Knight, and a Castle, respectively. First of all, they’re three different pieces, each of which moves in different ways and plays a different part in winning a chess game. This speaks to the ways in which the three characters help and strengthen each other by each bringing something different to their friendship. But perhaps even more importantly, the three pieces are relatively equal in worth, with the Castle being worth just a bit more. Making Harry the King would have been a good strategic choice, since he would be the most protected piece on the chessboard, but it would have elevated him too far above his friends and had them taking risks and making sacrifices for him, rather than for their common goal.
One last clue that Quirrell is not what he seems comes in the form of his obstacle: a troll. Earlier, Harry and the others assumed he had performed complicated defensive magic, but no, he just left a magical beast there, one that we already know whoever is trying to steal to stone has used in the past. Meanwhile, Snape – who you would assume to have left an intentionally easy challenge, if he’s working for Voldemort – instead created the most difficult one so far. Most of the challenges are dangerous or even potentially deadly, but there’s nothing quite like being presented with seven bottles, knowing that three are poison and only one can help you move forward, or that you have only your wits and a couple of vague clues to help you figure out which ones are which. Whoever makes it this far trying to steal the stone, Snape wants them dead.