Electro: Great stuff in the trailers, both before and after getting his powers. I've never been an Electro fan, but from what I saw in the trailer, Jamie Foxx would've had me for a movie of Electro against Spider-man all on his own.
Rhino: Random brute villain? Maybe, but it'd be a waste of Giamatti.
Green Goblin: From what we've seen, they're tossing Harry in there, telling us they're friends (oh, hey Peter, been 10 years, huh? We were so close back then, yeah, we're still totally bros) to try forcing a sense of tragedy to the conflict between them later in the movie. The last Spider-man 2 did that pretty well, but they'd already established Harry as a character.
All the other shit: there's already no room for it. The problem with stuffing these characters into a movie isn't their presence--it's that this movie will serve as the introduction for each of them. Spider-man does have a great rogues gallery, which is why the movie-makers shouldn't treat them like a mass of henchmen.