One of the big apprehensions about watching a Spiderman movie for me was how they would be able to reproduce the way the wall-crawler swings around with his webbing in a realistic "comic-book" manner. Thanks to the magic of computer graphics, the movie doesn't disappoint in that regard. As someone who has been reading Spiderman for over twenty years, and regularly go over several hundred back issues as interest permits, that alone was enough to make the film work for me.
The first part of the film is straight out of the first appearance of Spiderman in a comic book (Amazing Fantasy 15, the last one in the title for a long time until Marvel published three more continuity stories). The story begins when mild-mannered Peter Parker (Tobey Maguire) gets bitten by a radioactive spider (in the film, it's a genetically-enhanced spider). He soon discovers he's stronger, faster, able to climb walls by sticking to them, and possesses a "spider-sense" that warns him of danger. Being a brilliant scientist, he even develops a strong form of webbing to enable him to swing over New York City (in the film he can shoot webbing out of his wrist).
Faced with money problems (he is an orphan being raised by his Aunt May (Rosemary Harris) and Uncle Ben (Cliff Roberston)), the first thing he seeks to do is capitalise on his powers. In his rush to make money, he forgets his Uncle Ben's adage, "with great power comes great responsibility", and fails to halt a robbery that ultimately results in the death of his uncle. Faced with the consequences of the choice he has made, he decides to forever use his powers for good. Not everyone trusts him, however, and he ends up being scape-goated by the Daily Bugle's publisher, J. Jonah Jameson (J. K. Simmons). Ironically, Peter Parker works as a free-lance photographer at the Bugle since he can capture pictures of most criminal activities first hand (as they are thwarted by Spiderman).
A theme (espoused by Jameson) in the Spiderman books is that he's considered a menace simply because he is a superhero. He is a magnet for supervillains that cause wanton destruction of life and property. Over time, this leads to great introspection by Peter Parker, but ultimately he decides to don his costume again and swing for another day. One of his most famous villains is the Green Goblin, aka Norman Osborn (Willem Dafoe), whose origin is also chronicled in the film. Unlike Peter Parker, Norman Osborn decides to use his powers to go against Spiderman, and in doing so, ends up threatening the life of his aunt and his new romantic interest, Mary Jane (Kristen Dunst).
The changes the movie makes to the original Spiderman character is worth thinking about: it makes more sense that a genetically-enhanced spider, containing traits that is an amalgam of other spider species', endows Peter Parker his powers. It doesn't make sense that his webbing shoots out of his wrist, particularly without some sort of a metabolic explanation for how it is created. In terms of plot, the film ditches the character of Gwen Stacy, Spidey's "first love", and merges a comic book storyline about her into the film. (Gwen Stacy died by falling off a bridge as Spiderman and the Green Goblin fought each other in Amazing Spiderman 121.)
Tobey Maguire does a great job of playing both the mild-mannered Peter Parker as well as the amazing Spiderman. Comic book readers are used to an older Spiderman, but it's important to remember that Peter Parker was first an high school student before he had to deal with the real world. Maguire does a great job in capturing his earnestness. It's also clear that Maguire has studied the comic book well: his actions mimic how we'd expect Spiderman to move. The film works in large part due to his ability to project the same feel that readers of the comic books are used to (the rest of the film, particularly the computer graphics, complements his motions well also).
For the record, Mary Jane is currently dead [she later was found to be alive] after marrying Peter Parker. Aunt May is still alive (and has just discovered yet again that Peter Parker is Spiderman), though she has gotten better from terminal conditions quite a few times. I can't wait for the clones and the all other villains to attack. I definitely recommend checking this film out on the big screen.
The Spiderman movies have definitely changed the story from the comic book. Watching the first of the film , I wasn't happy with the depiction of Peter Parker as more self-centred and vain, which is unusually in the context of the comic books. At this moment, Peter Park goes through so much crap that it's a wonder he doesn't commit suicide (it's kind of like Jack Bauer in 24).
Some factual points that were changed, which I'll agree was necessary to make a decent movie, are as follows: The Venom costume is an alien being acquired during the Secret Wars battle with the Beyonder (which was one of the best "cosmic" series Marvel has put out). Spiderman doesn't want to kill villains; even when he is beaten and pulverised, he holds back from taking the ultimate step (in fact, it is rare to show people dying in the comic books). Harry Osborn is more like the depiction of Normie Osborn (the son of Harry and Liz Allan) who is friends with the daughter of Spiderman (Spidergirl). Gwen Stacy is killed by the first Green Goblin (Norman Osborn). The people of New York have rarely been on the side of Spiderman. J. Jonah Jameson has always had a point in saying that it is people like Spiderman who create the villains. And so on.
It's difficult for me to reconcile what I know of Spiderman's history with a movie story that does its best and I admire that. A problem with the movies is that they can't intersect with the other characters from the Marvel Universe. It would be great to have movies like the Secret Wars or the Infinity Gauntlet, War, and Crusade series where a bunch of the Marvel superheroes get together and the stories make more sense (for example, explaining the origin of the Venom symbiote), but I guess that would be a logistic and budgetary nightmare.
Halfway through the movie, the story gets in line with what you'd expect from the book. The rejected symbiote bonds with a humiliated Eddie Brock to become Venom, one of the coolest villains to be introduced in the later years. The Sandman is a villain who is ambiguous. And Spiderman has a run of bad luck and is pummeled constantly but triumphs in the end against all odds.
I once wrote a review of the Batman series where I connected them to a lot of the comic books (I own a huge number of Spiderman comic books) and some other reviewer criticised my review. The perspective I offer is fairly unique: it is based on an experience I can't ignore or negative, and I think it helps place the movie in context of a long history of the books. So if you're interested in the saga of Spiderman beyond what you see in the three movies, I recommend buying some of the great story arcs of Spiderman just to see how complicated and mythological the creations are.