It is extremely difficult, if not impossible, to translate a book into a movie. The problem has to do with one's imagination: words in a book conjure up images that are highly personal and subjective, and any attempt by a third party to lend form to them ends up disappointing. Harry Potter and the Sorcerer's Stone is no exception in this regard, but fortunately, the imagery presented is awesome and wondrous in its own right.
The film is made strictly by the book: Harry Potter (Daniel Radcliffe), a young boy mistreated by his foster family, learns that he is special and comes of age... in the Hogwart's School of Magic (!) where he learns wizardry, plays Quidditch and fights an evil despotic wizard (who does not turn out to be his father).
While the movie stays fastidiously true to Joanne Rowling's book, perhaps one of the best adaptations ever, the adage that a picture is worth a thousand words doesn't hold true here. For the most part, from the initial victory of the baby Harry Potter upto the Quidditch match, a lot of the details are skipped. What we're presented with is a jump from one scene to another (sometimes too quickly) that illustrates with painstaking effort the magical realm that Rowling has constructed in her series. For example, while the opening sequence shows Professor Albus Dumbledore (Richard Harris) turning out the lights in a street, Professor McGonagall (Maggie Smith) changing to her true form from being a cat, and Hagrid (Robbie Coltrane) bringing Harry on his flying motorcycle, we're not really shown the celebration of Lord Voldemort's fall. This isn't criticism but just an observation; in fact, I think doing this is especially okay if one is familiar with the Harry Potter books, but it does impart a sense of urgency in the beginning portions of the film.
I marvelled at how technology enabled the film makers to make possible the wonders of Harry's world, including Diagon Alley and Gringotts Bank, the moving pictures, Hogwarts Castle, the Sorting Hat (Leslie Phillips), the ghosts in the Castle (including a cameo by John Cleese), Fluffy the three-headed dog, the ugly troll, and so on. I believe that it is technology that makes the Harry Potter film authentic, in the same way as in the X-Men or the How the Grinch Stole Christmas movies, by letting at least the imagination of a few people come to life as vibrantly as possible. Most of what I imagined and what was projected on the screen weren't really colinear, but it was still cool, incredibly so at times, to watch.
The movie, however, picked up with the first Quidditch match where Harry, on a broomstick, plays the position of a Seeker after the Golden Snitch, a particularly hard-to-catch ball, which is key to winning a game. The inspired depiction of the game meshed with my imagination extremely well, and from there on, the story of Harry's second encounter with the dark Lord Voldemort (Richard Bremmer) enfolded in a less fragmented and more cohesive manner. The final confrontation, and what Harry and his friends have to do get there, is a delight to watch.
For those paying attention, the main change from the book has to do with how Hagrid's dragon is disposed of and the resulting consequences. The ghosts also play a smaller role here though given the movie's running time, I'm not surprised parts like those were omitted.
The actors playing the young leads give decent performances, with Emma Watson as the know-it-all Hermione Granger standing out. The adult actors aren't given much time but they all present solid performances. The score by John Williams is simple but effective. The set design, cinematography, and visuals are impressive. Director Chris Columbus does a great job of bringing to the big screen the Enid Blyton-like atmosphere that Rowling's books exude.
Harry Potter and the Sorcerer's Stone is a great movie to watch. I viewed it from the perspective of someone who is intimately familiar with the books, and I believe there is strong merit to watching it being completely unfamiliar with the story, a choice I do not have given that I've read the four books a few times. Definitely check it out on the big screen and make sure you goto the bathroom before.