That proof of concept looked fun but from a game design perspective there are a few problems:

- That level is very open and disorienting. Where are you supposed to be going? What are you supposed to be doing? You don't really know until you (unintentionally) make it to the goal post. Sonic games had multiple paths but were always directional. You never ended up back at the beginning by total accident. The game always had a way to move the player forward.

- The design on the enemies is terrible. Why do people think that Sonic needs to awkwardly fly around trying to hit lots of tiny insignificant enemies? I would rather Sonic fight fewer but much larger and more substantial enemies (almost like mini-bosses). That way each one poses a challenge.

- Level is a bit boring. Yeah, some of the slopes were exhilarating, but most of the level was flat and unappealing. He was just running around in empty space.

Let's take a step back here. What made Sonic in 2D fantastic (yes, armchair game critics, the Sonic formula was, and is still fantastic... deal with it) are the so called "three pillars" of Sonic: speed, platforming, and exploration. It's not just that Sonic had these things separately at different parts of the level. Each of these things worked TOGETHER during gameplay providing an experience that was very different to other platformers.

Can a 3D game have all three of these attributes working together? Yes. Quite easily, actually. It's been done before. Just because the series has fumbled through glorified tech demos (The Adventure series) and what has essentially boiled down to a less fun version of futuristic racers (the boost gameplay) doesn't mean the series is incapable of producing an incredible game.

Think about what made Sonic's gameplay work in 2D: the physics. It was the glue that stuck everything together. Sonic's physics made total sense to anyone who had ever played pinball before. Sonic behaved like a pinball: he would fly through slopes and bounce just as these old games would. Simply recreating these physics in 3D would be terrible. It would be confusing and disorienting... God help the poor sap who would attempt to design a camera system for it. A compromise will have to be made, just like the compromises made bringing Mario into 3D. Instead of going back to pinball physics for 3D, let me propose another type: snowboarding physics.

Think about it. The player needs to constantly work to maintain speed using the environment while avoiding hazards to get to the end of the level. While snowboarding games often have only one path, why can't this theoretical Sonic game have multiple? Why can't the whole level be filled with slopes and places Sonic can reach if he's gained enough speed? Levels don't have to be open world. Just open enough to present the player with choice on how he or she wants to tackle obstacles.