It seems like someone at Marvel (sorry, Sony) decided that they were going to make the funniest film they could. I'd say they pretty much succeeded. This follows in the footsteps of Deadpool, but with a bigger budget and rather more in-universe recognition.
The humour comes rather naturally from the setting of the Spider-Age at a mid-teen. It's an excellent idea that allows the film to really distinguish itself from the previous...six? and let it find its own level. It allows us to see a much more incompetent Spider-Boy, and allows the emotional notes to hit nicely. Tom Holland does young rather well.
The other characters are also twisted just enough to make them fresh. MJ may or may not exist as MJ, but she's a fantastically sarcastic bugger. Flash is still a git, but it's more believable coming from a child. And Ned is a slight spin on an Ultimate character, and provides the enthusiastic response needed.
Which does stand in contrast to the Liz plot. I can't decide whether that needed more time or less. It felt a little more bolted on than it needed to. Part of me wonders if you could do Spider-Man without a romantic subplot.
Everything beyond that subplot held together very nicely though. Michael Keaton was brilliantly cast as the villain, and all the other villains sneaked into the background added a few nerd bonuses. They also slotted neatly into the overall universe, and the workmanlike appearance of weapons (and the Vulture) felt very believable.
And that extends to the various bits of other characters dropping in. It's entirely possible to imagine Cap doing a range of videos for school children (and that was a fun stinger). Downey is still obviously having fun playing Stark. Just a shame they couldn't sneak Jarvis in.
Luckily we got Karen, the Spider-AI, who was so much better than the Alex of Valerian, which so disappointed me two days ago. We're living in a world now where AI tend to be a slightly sarcastic dry wit (while still helpful) and I tend to miss that when it's done poorly.
Overall though, an excellent addition to the Marvel Universe, and I look forward to the next one.