Spectacular Spider-Man was perfection! Though the movies and comics are allowed to have darker moments, of course!
The lightheartedness were signature aspects of Buffy and Avatar too. Look what happened to the Last Airbender movie when the lighthearted nature of the series was taken away from it!
And like Agent Z said, USM is too superfluous with no real gravitas. The Spectacular Spider-Man got the tone just right.