A)Harry Osborn returns. Norman Osborn is sick and Harry Osborn takes Oscorp over. Now we see Harry Osborn true side. He is making Sinister Six in Oscorp. First, Harry Osborn shows pictures to Peter about Peter and he says: See, that´s you in Oscorp. Peter looks with frightened face. Clearly, Harry wanted to see Peter face to be sure that he is Spider-Man(cameras in Spider room). Also when Harry showed those Pictures to Parker, then Harry had funny and happy voice(with evil smile). Look at Harry evil face.
(ALSO, DO YOU SEE THAT HARRY DARK EYE CIRCLES??? – DRUGS???)
Well, in Comic Con trailer Electro says: "I just wanted everybody to see me."
Harry Osborn says: "You will never be invisible again"
This clearly shows that Harry Osborn created Electro. Also, later we see Electro with chip on his head. This means Harry Osborn controlls Electro. Electro has Oscorp suit, this proves that he gave even a suit to him. Also, later we see Rhino big robot in New York, this is also from Oscorp. So, Harry Osborn is bad guy. Harry clearly wants revange because Peter is Spider-Man and Harry is nobody. Also Harry feels betrayed by Peter because Peter never contacted with him before. So, when Spider-Man beats Rhino and Electro, then Harry turns into Green Goblin. In this or TASM 3 Harry Green Goblin will kill Gwen Stacy. If you can´t kill Spider-Man, then you can kill his girlfriend. So yeah. Harry has more reasons to kill Spider-Man and Gwen Stacy than Norman Osborn.
In short: Harry Osborn leads Oscorp, and he do bad stuff while his sick father Norman Osborn knows nothing what his son is doing.
B)Harry Osborn returns. Norman Osborn is sick and Harry Osborn takes Oscorp over. Harry and Peter Parker are best friends. Harry Osborn invites Peter in Oscorp and shows pictures about him and he says: "Oscorp has been watching you."
Peter: "Why?"
Harry: "Good question"
So, Harry knows that something is going on but he has no idea why Oscorp has watching his best friend.
Later in trailer Harry says: "What is this?"
Norman: "The Future"
Harry: "We really can change the world. What will happen to Peter?"
Norman: "A happy ending isn’t awaiting all."
So, this means Harry Osborn finds that Oscorp has making villains like Electro and big Rhino. Norman tells truth about Oscorp. Norman tells that he has to kill Peter Parker becuase else he ruin his Oscorp plans. So, Harry finds out his father dirty secret and does not want to kill his best friend. Harry refuses to do that, and then Norman also lets test new cure on Harry which makes him Proto-Goblin. So, Harry Osborn is victim. Yes, Harry Osborn is Proto-Goblin. His father used serium on his own son because Harry and Norman views are different.
In short: Peter and Harry are best friends. Harry discovers his father dirty secret. Harry refuses to do what his father wants and then Norman Osborn forces Oscorp to test new cure on Harry Osborn. Harry Osborn is Proto-Goblin.
C)Well, everything is same as B, but instead when Harry discovers his father secret, then Harry Osborn agrees with his father views. To protect Oscorp, Harry is ready to test Goblin serium so then he can kill his friend Peter Parker.
In short: Harry Osborn is ready to kill his best friend because he thinks Father is doing the right thing.(Also Harry wants this Oscorp futuure)
So, which version you want to see?
A)Norman is sick. Harry is evil, young and greedy. He want´s his revenge.
B)Norman is bad guy and Harry is victim who turns into Proto-Goblin.
C)Norman and Harry are both bad guys.