Positive = While they eliminated the whole Gwen Stacy thing, otherwise they did a pretty solid job of sticking to the comic book's origin for Spider-Man. From "with great power comes great responsibility" to his first wrestling match, they made a solid attempt to appeal to the fans.
Negative = The film felt a tad rushed because they had so much to get through in order to reach the final confrontation with the Green Goblin. So many things didn't make sense in the plot because they wouldn't take their time to explain it properly or let the characters develop in a logical way.
Positive = They made some really brilliant casting decisions in a few roles that I could not imagine going a different way. J.K. Simmons is the perfect fast-talking J. Jonah Jameson, Willem Dafoe is delightfully menacing as Norman Osborn, and Kirsten Dunst is a charming love interest who manages to sell some not-so-great lines of dialogue.
Negative = The CGI and green-screen work is not good and has not aged well. You can always tell when they make the transition to effects and it stands out like a sore thumb.
Positive = They did some action sequences using practical effects, and those were really well done. The costume for Spider-Man looked pretty great, and therefore any still shots or practical stunts were excellent.
Negative = The Green Goblin's armored suit is horrendous. He looks like a character plucked right out of a Power Rangers episode, and doesn't belong in the same film with that good Spider-Man suit. Also it takes away the joy of seeing Willem Dafoe's villainous snarl, which might be the best one you'll see from any actor in Hollywood.
Positive = I like how they touched on the fact that Peter Parker has a tendency to over-extend himself trying to do too much at the same time, but they didn't belabor the point and make it the focus of the whole film. The simple passing references to getting fired from Dr. Connor's lab for always being late was enough for us to know what's going on without having to see him constantly annoying everyone with his tardiness.
Negative = Remember how I said they made some great casting decisions? Well the most important one is where they really dropped the ball. I cannot stand Tobey Maguire as Peter Parker/Spider-Man. It's hard for me to explain, but his dweeby personality just doesn't fit. (Peter Parker was more of a Nerd or Geek, not a Dweeb, and there is a difference.) I don't like his child-like voice coming out of Spider-Man, and I cringe whenever you actually see his face and are supposed to believe he's in a fight scene with full-grown adults. He also feels like a complete mismatch with Kirsten Dunst, and they have no chemistry, despite her best efforts to sell it. James Franco isn't much better, but I won't get into that.
When I tally it all up I think I still lean a little towards the side of disliking Spider-Man, but at least now I can understand that there are good qualities that make other people like the film.