Blimey. I played this so much today, I got to the end.
For the sake of brevity, and also to avoid spoilers, here is a condensed version of the events of the day:
Mysterio called me to his “underground lair”, which was a funhouse. Killed deformed mirror versions of myself. Went to Octavius’ presentation, machine went loopy, his wife died, arms got fused to him. Dr. Octopus attacks the bank, I chase him off, he takes Aunt May, I chase his helicoptor, etc. More Black Cat chases. Find Shocker, and fight him with Black Cat. He escapes, but find him later for another fight. Run into Mysterio again, but he was really easy this time. Some Peter-and-MJ stuff happens. Destroyed some mech things with Black Cat. Fight Dr. Octopus on a train, then in a warehouse. Final battle is bloody hard, then the game is over and the (very, very lengthy) credits roll. Hurrah!