This film is OBVIOUSLY one big feature-length setup to a sequel... So much so, that it's like "why even make this movie, why not just skip to the sequel".
My only guess is that the other Spidermans had advanced too far in Parker's age. They'll get more audience appeal with reinventing the high school nerd finding powers and falling in love story that's baked in to his origin.
I agree though, they should've just jumped right in with whatever they have planned for the sequel
[spoiler - click to view]
The origin story setup and "discovering spiderman" montage wasn't different enough from the other movies to warrant spending the 1st hour on it. It was well done and entertaining but I feel the same way.