They could've done alot more with Harry in this movie.
They could've did so much more with Harry's character. I also felt they killed Norman off in the movie WAY too early when he could've been used alot more.
Instead of having Harry find the cure for himself, I would've had him find the cure for himself and Norman in an attempt to finally gain acceptance from his father. I would've also had a scene of Harry going to the doctor to find out that the disease is also killing him at a much faster rate than it was killing Norman just to clear up some confusion people had with the actual film. Harry then asks Spider-Man for some blood, he refuses (just like in the movie) and Norman dies shortly after. Harry becomes furious and he finds out about the spider venom (just like in the movie) and he becomes the Green Goblin.
I also would've tied him in with Peter and Gwen. I would've had Gwen become friends with Harry after she breaks up with Peter (without her knowing that he was childhood friends with Peter until later on in the movie). He likes Gwen but Gwen basically friend zones him as she still likes Peter plus she's leaving for Oxford. That would've made the final battle in the Clock Tower alot more meaningful as opposed to what they did in the actual movie.