Many of the backgrounds used in the cartoon might look familiar: they were recycled from the original 60s cartoon.
The original voices for the cartoon were added via text-to-speech software as a placeholder. This meant the actual voice over work by the actors had to be lip-synced in post-production and caused nearly a weeks worth of work to match the voices to the mouth movements.
Spider-Man doesn't have webbing or a spider on his costume as it would have been impossible to replicate due to software and time limitations.
During Spider-Man's hallucination, Deadpool was going to explain in greater detail why "None of this is real" and physically show him by walking outside of the cartoon, that they were just in a badly animated cartoon on Youtube. This scene was not created due to time restraints.
Creator Vaughn Smith known as Moxxi re-recorded 8 cover versions of classic Spider-Man music (the originals were never found) from the 60s cartoon in 2007. They are available on iTunes.