One thing I think he missed out on was a discussion of level design. What made the 2D Sonic games work so well wasn't just speed, it was about levels which were constructed specifically in ways that allowed you to move fast and survive with split-second reflexes. Things were set up specifically so that, if you were good, you could get through most levels without ever really slowing down or stopping (especially in Sonic 2 and 3), and often reflex action would take you farther than thinking too much about a given scenario.
This is also why I hated the Sonic Rush games - they were fast to a fault, with level design that required you to take your time and move slowly. Instead of being able to reflex your way through, most of the time that kind of behaviour would just get you killed. It just wasn't fun, and to me is proof that 2D isn't a recipe for speed working - you still need the rest of the game to actually accommodate that aspect of play.
Otherwise, great video. Didn't touch as much on raw mechanics as I expect but still a very nice analysis and really captured the spirit of what made Sonic work and not work over the years.