It's a shame, then, that the game itself plays so uninspiredly. The low level of difficulty is understandable; this game is geared towards children, after all. The uninspired level design and repetitive gameplay are not so forgivable, however, and the painful flight control scheme makes what could have been an exciting part of the game more frustrating than it should be. Add to that a few more questionable design decisions, and you have a game that misses the mark that it aims for.
The storyline of the game diverges rather widely from that presented in the book and the movie, but it's close enough to be recognizable. You'll spend the first significant part of the game learning new spells and trying them out in different challenges; why none of your classmates go on these challenges with you is left completely unexplained. You'll recognize many characters from the Harry Potter mythos, such as Ron and Hermione, and the various teachers.
The game plays like a simplified action/platformer. Think a child's version of Tomb Raider, and you'll have an idea of how it works. Harry can move around, jump, and cast spells--if jumping is too difficult, the game features an 'autojump' to make it playable for younger kids. The spell is always context-sensitive; point the sparkly magic bits at what you want to affect and the game will choose the proper spell.
Although the story is far from the books, that's understandable, as you need to add enough content to make the game workable. However, the execution of it all leaves much to be desired. For example, you learn spells by tracing their patterns on the screen with your mouse. This is frustrating, even for someone with good mouse control, and many kids will find it difficult to do it both rapidly and accurately. The game awards house points for successfully completing goals, which is a nice touch, but there are some serious logical flaws in it--when Hermione says that Professor Sprout would 'surely give Gryffindor ten points for that,' how does the House actually get the points? Was Sprout watching? This is probably something that wouldn't phase kids playing the game, but as someone who is steeped in the lore of the Harry Potter world, Harry Potter and the Sorcerer's Stone makes some glaring jumps like this.
Perhaps the most frustrating thing about this game, though, is the way that it limits you. Instead of being able to wander about and do your own thing, you're always on the run to a class, to a challenge, to something else. It never felt like I was actually in the gameworld; it felt like this was some sort of funhouse Hogwarts, which existed merely to torment my Harry avatar by throwing challenge after challenge at him.
And what could have been the coolest part of the game--flying, and the requisite Quidditch--ends up being confused and unexciting. The flying controls provide none of the grace and speed which were presented in either the movie or the books, and Quidditch ends up being just another challenge to complete.
In all fairness, there are some nice touches spread here and there throughout the game--I like that you collect Bertie Bott's Every Flavour Beans, although I don't like that they hide inside of trees and armour and the like, and the use of spells from the books (although I don't recall Flipendo, and a quick look in the Lexicon makes it seem it was created for the game) is quite cool. And the Invisibility Cloak's turn in the game is thoroughly enjoyable. It's just that the game could have been much more than the run-of-the-mill platformer that it turned out to be.