Sins of the Fathers Chapter 6: Framed - S3-E6
Plot hole: After Peter Parker is framed and arrested for selling government secrets to foreign organizations, he escapes police custody and goes home to retrieve his Spider-Man costume that was simply hanging in his dark room. If he was arrested for selling government secrets then surely the police would have searched his home and found his costume (as well as equipment) in the process. Since the police car was visible in front of his house, it seems very strange that police didn't search his home.
Six Forgotten Warriors Chapter 5: The Price of Heroism - S5-E6
Plot hole: This series is in the same continuity as the other Marvel animated series from around the same time - X-Men, The Incredible Hulk, Iron Man, and Fantastic Four - by virtue of each aforementioned show crossing over with at least one of the others. This episode, which originally aired on October 17, 1997, establishes that Captain America had spent the last 50 years locked in another dimension with Red Skull, and the episode ends with he and Red Skull once again becoming trapped in the aforementioned dimension. However, the final episode of Fantastic Four, entitled "Doomsday," which originally aired on February 24, 1996, features a cameo by Captain America in the present day, attempting to stop a rampaging Dr. Doom.
Sins of the Fathers Chapter 7: The Man Without Fear - S3-E7
Plot hole: They forgot Daredevil can sense when someone's lying, one of his powers. So, he should've known Spider-Man was telling him the truth about the computer disk.
Partners in Danger Chapter 10: Lizard King - S4-E10
Plot hole: When Debra and Margaret arrive at the underground arena with the device that can revert the humanoid lizards to their original forms, they lose control of the device and it ends up in the hands of Ghila, who monologues that the humanoid lizards' existence was an accident and that she will use the device to return them to being regular lizards. Ghila had never seen this device before, nor did anyone tell her what its purpose was, so there's no way she could have known it was designed to reverse the mutations.
Partners in Danger Chapter 9: The Haunting of Mary Jane - S4-E9
Plot hole: Miranda Wilson states that after the accident on the movie set left her face disfigured, she hid in the catacombs by the bridge and almost died from her condition until Quentin Beck found her after he was released from prison. Beck is the one that caused the accident in the first place, so even if he only spent a month in prison, Miranda Wilson would have died from starvation or malnutrition - if not infection from her untreated facial disfigurement - long before Beck could have been released from prison and found her.
Answer: Yes. Many things that would have been in the sixth season would have had Norman Osborne returning from limbo and reclaiming the title of the Green Goblin, Richard Fisk, the son of "The Kingpin" Wilson Fisk would return as a crime lord known as "The Rose", Ghost Rider would have appeared to help Spider-Man stop Dormammu from returning to Earth and Madame Web and Spider-Man would rescue Mary Jane from limbo.