Here's just some ideas...
Peter is still broken from the loss of Gwen. He's haunted by dreams and visions of the two of them, living together & happy. Rather than deal with this, he pushes himself into Spider-Man work. This threadline permeates throughout the movie..."Peter Parker, No More."
With more Spider-Man action, there's more pictures to take--Peter's working steady freelance for Daily Bugle (Introduce
JJJ, Robbie, Betty, etc.)
Near the film's beginning, I'd have Spider-Man take down a small band of robbers (easy intros for characters like
Flint Marko, Enforcers, etc.). He's being monitored by
Spider-Slayers silently surveying the entire city.
Gustav Fiers & Smythe watch the feed & study Spider-Man's movements & style from Fiers' new CEO office at OsCorp. Fiers is essentially
Harry's eyes and ears, as he reports to Osborn in Ravencroft about the outside world (so Osborn has "plausible deniability").
The plan is to use
Chameleon to impersonate Spider-Man and frame him, ultimately turning the city against him. Osborn has him attack a major gala/event where JJJ and the Mayor are in attendance. Spider-Man vs. Spider-Man...enough doubt is raised where public opinion turns & Spider-Man deals with the hate.
Now, he must wonder. "No more Peter Parker...now, no Spider-Man? Identity crisis"
Mysterio would be an additional villain in the story, though I'd keep his origin separate from OsCorp. Quentin Beck and
Phineas Mason (Tinkerer) create the elaborate Mysterio to counteract the new villainous Spider-Man (Chameleon). **Lots of illusions, smoke, explosions, & somehow include illusions of Gwen, Ben, parents, Capt. Stacy, etc.**
Mysterio starts trying to plot destruction in order to appear heroic, so Peter/Spider-Man must realize who he really is and stand up as the city's true hero, restoring his tarnished reputation, moving on from his guilt, and fighting Mysterio & Chameleon.
Additional:
Mary Jane is present in movie.
Aunt May notices Peter slipping deeper away and tries to set the two up. MJ offers him an anchor and a shoulder to cry on.
Spider-Man sneaks into Ravencroft and confronts Harry about Gwen's death (and to interrogate him on his involvement in Chameleon and/or Mysterio).
Maybe a
Black Cat sequence where Felicia, hired by Osborn, breaks him out Ravencroft...setting GG up for TASM4 with the Sinister Six (GG, Ock, Mysterio, Electro, Rhino, Vulture).
Visual Ideas....
Maybe go bigger on the fish helmet, but Mysterio's look should very much be updated (keep green & purple hues, though).
Chameleon should be an ordinary man underneath his Spider-Man costume, though he develops an almost "stalker" vibe for Peter / Spider-Man...becomes consumed with replacing him.
He should also use OsCorp gear that simulates the Spider-Man powers (increase strength, web shooters, etc.)
Rough idea for initial Spider Slayers.
Black Cat