I _did_ really enjoy his video, but I think what he addresses as criticisms are very difficult for me to see as such.
First, the bosses. I know you were suddenly confined to a smaller space with no way to recharge your rings, but Mega Man did the EXACT same thing, and I consider Sonic's bosses to be a lot more creative than that. Beating them comes down to mastering skillful movement and timing, which is EXACTLY what being great, rather than good, at a Sonic game is all about.
But I get what he's saying. Sonic games lose accessibility as they go on. Anyone can blast through Emerald Hill and have a fun time, but by the time you hit Mystic Cave, that same newbie will be slamming into enemies constantly, losing rings, losing flow, and getting more and more frustrated.
Another good example of this is shown when he's talking about the water levels, and how you have to be "lucky" enough to find a bubble. He dies, despite the fact that a bubble just spawned right above his head. It's not really about luck... those bubble spawners all make big bubbles at the same rate. Had he mastered the timing of them, he'd have jumped earlier and survived.
I think the problem, then, is that "mastering skillful movement and timing" simply isn't something you HAVE to do to get through the game. At no point, until those tough-as-nails end bosses, does the game ever impede your progress completely. You can slam into enemies, pick up a few rings, and limp through to the final level. Then, because you were never expressly DIRECTED to do anything but blindly push ahead, you'll lose all your lives to the final boss because you never became skillful.
But Sonic isn't about winning. Sonic is about mastering the flow of the game. That's exactly WHY the early levels are so quick and easy to breeze through... it's a game that you're meant to come back to again and again, getting better and better each time. That's the "arcade" style mindset taken to its best conclusion. It's why 19 years after getting Sonic 2 for my birthday, I can still fire it up and have fun with it.
That kind of game simply isn't _for_ everyone, though, especially not if you're more into the idea of "games-as-experiences." There's nothing wrong with a game being more about the experience than the game, of course. I just beat Bioshock Infinite, and I adored it. But Sonic, even NOW, is more about the mastery of the mechanics through trial-and-error.