I'll start off by saying I liked the movie.
Now, I don't know if it was too much trailers. But I think if they hadn't tipped their hand with Harry being the Goblin and there being a Rhino scene in the movie, it would have been a big surprise factor and really been a huge point of emphasis.
Imagine going into the theaters thinking Electro is the focal point of the movie while knowing that Harry Osborn was playing a role too, but you had no idea Harry would turn into the Goblin and you had no idea that the movie would end with the Rhino scene. I think they showed too much. If they would've done what I just said, I think more people would've been pleasantly surprised.