I don't have issues with diversity, but this movie tried too hard. Every other scene screamed "Look! MINORITIES!" They should have toned that down, and just keep it natural.
Peter was obnoxious as fuck and hardly even likeable. He could be troublesome when he began as Spidey, but even back then he had his reasons when he messed with the F4 (he needed money to support May and himself, since Uncle Ben died).
The supporting cast was terrible. Ned was the typical case of a "minority best friend comic relief" character. It was annoying in Ant Man, it was even more so here, especially because Peter should have gone lengths to prevent him from getting involved, since it was really dangerous.
Iron Man took far too much agency from Spiderman. Sure, he's 14, but Peter has always been his own person. He makes his mistakes and figures things out on his own. Sure, he's had mentor figures like Reed and Tony, but that's that, his agency was always his.
In this movie Peter just kept screwing up, hardly ever taking some time to reconsider his own actions, all because he wanted to become an Avenger.
I didn't like him getting a cybernetic suit either. Sure, in some stories he's had special suits, but since this is his beginning as a hero, he should just have a regular costume.
Flash looked all sorts of retarded. He was more of an annoying nerd, than a bully and he wasn't even a jock. Those two things have always been aspects that defined his character (when he was young).
Not having Peter recall Uncle Ben once, and the deal about the responsibility that comes with power, even if it's been done several times now, is a shame, since that's always been an important factor for Spiderman.
Gwen and Mary Jane should have been there, considering how crucial both of them are in Peter's life.
Vulture was the best thing in this movie. He deserved a lot more screentime.