JK Simmons said in an interview, I think it was to AV Club, that the studio pretty much threw out the script and made them add and change things on a daily basis. That's why it feels like such a colossal mess, because even the cast and filmmakers had no idea what they were doing and how they were going to put it all together.
But I'm definitely with Kulap. I didn't think it would be possible to make a worse Spider-Man movie than Spider-Man 3, but Amazing Spider-Man was probably worse. It had similar, but not as obvious, script issues but, man, was it more boring than a dog's ass.