Spoilers lie ahead, so be warned:
The Good:
Like in the first movie, Spider-Man looked terrific. There were fewer hero poses, and aside from a few spots here and there, the CGI looked great. Beyond the CGI, they will never find a better actor to play Spider-Man - Garfield is beyond good, he's perfect. And while I'm just talking about Spider-Man, he's greatly improved as Peter Parker, as well. As almost all the reviews have said, Garfield and Stone have great chemistry - I'd watch them together in anything. In fact, I'd prefer to watch them in something else.
I can't put Electro in the good camp, but the Times Square scene was great. I also thought Dane DeHaan was very good as Harry. Felicity Jones - Would Do. For the most part, the movie was a lot of fun.
They did an absolutely terrific job foreshadowing Gwen's Death, then making it seem like they were going to cop out of it, then slowing the movie down just long enough for the whole audience to catch up and realize "Oh no, they're really going to kill her." There is a feeling of hopelessness that is absolutely terrific. It plays out really well within the movie. Even the web hand thing works. I especially liked what they did with Dennis Leary.
The Bad:
The script. I really don't even know where to begin. I don't mind spoilers, so I read a synopsis of the movie before I saw it. It detailed 11 different storylines. There were more. And none of them really tied together. There was a staggering amount of random crap in there that could have been cut. (Aunt May is secretly taking Night-Nursing classes!)
Electro's powers made no sense at all - there is a scene involving planes that will have leave many people shouting "What the Heck, Movie"? The worst part about it is there was no reason for that scene. There was plenty of other stuff going on.
Gwen was a delight every moment she was on screen, but her role in defeating Electro was preposterous, even by Comic Book Movie standards.
The Green Goblin was very rushed. (He is on screen for maybe two minutes.) So rushed that all of his scenes looked like they were in weird fast motion. DeHaan (and all the actors really) did a very good job with the horrifically bad script he was given - until he became the Goblin. He was laughably bad. I was glad to see that they "normaled him up" a bit at the end, because while he had a great presence as Harry, he had none at all as the Goblin. It just didn't work.
The music was horrendous. I don't know what they were thinking. It felt like they made music without knowing anything about the movie except how it ended. I expect a lot better from Hans Zimmer. Too many hands in the pot, I think.
The Ugly:
The Untold Story: Sometimes you dig yourself into a hole. When that happens, there's two ways you can handle it - you can climb out of the hole, throw dirt back into it, cover it up with some stuff and hope nobody notices you dug it. Or you can keep digging and hope you come out in China. They chose to keep digging. And digging. And digging. And digging. And there is no payoff. Well, scratch that, there are two things that we learn, and both of them are so terrible it hurts my brain to even try to put it into words:
1) Peter learns his dad loved him.
2) Peter learns that his dad's Spider-serum will only work with Parker blood
That's it. That's the whole untold story. Now I understand they had to tie up that loose end from the first movie, but they spent something like HALF of the movie on this, and that's the payoff? Really? Honestly, I think it was literally half of the movie.
To wrap it up: I can't stress it enough - No comic book character has ever been portrayed on screen better than Spider-Man was in this movie, and that makes up for almost all of the movie's other sins. He's so likable he makes the movie likable. I'm surprised to say it, but I liked the movie, even though it was a horrible, stupid, overlong mess.
I guess I'd give it 2.5 stars out of 5.