To illustrate my point a bit further, look at Sonic Colors' Sweet Mountain speedrun:
Stages were pretty well designed, and they were designed for you to be fast on them. Sure, there are a few "scripted events" or supposed-to-be-obligatory things that were supposed to make you go faster but only drags you down, and you can see the player avoiding some of these in the video (can we also please ignore Stage 11? It's a dumb level anyway), but notice how to speedrun levels, you don't just need to hold the boost button to win, you need to know very well the level design, and you need to use a bunch of Color Abilities, too. If the stages weren't designed pretty well, we'd just see Sonic boosting forward forever, avoiding rails, curves, color abilities, or anything else that'd keep him from just boosting forward - but we see some legitimate showcase of skill here.
I'm not sure how I feel about Modern Sonic's gameplay on Generations though. His gameplay was sorta repetitive in Unleashed, since most levels relied mostly just on boosting and avoiding things, having little variety to it, and I really enjoyed Colors because it added really good level design, a whole lot more platforming to it, and the Color Abilities, which opens a whole lot of variety to it. Modern Sonic though, will not have that much platforming, and will not have the Color Abilities (unless in Planet Wisp maybe?), so it pretty much counts only on a better level design that has more variety to it.
Stages were pretty well designed, and they were designed for you to be fast on them. Sure, there are a few "scripted events" or supposed-to-be-obligatory things that were supposed to make you go faster but only drags you down, and you can see the player avoiding some of these in the video (can we also please ignore Stage 11? It's a dumb level anyway), but notice how to speedrun levels, you don't just need to hold the boost button to win, you need to know very well the level design, and you need to use a bunch of Color Abilities, too. If the stages weren't designed pretty well, we'd just see Sonic boosting forward forever, avoiding rails, curves, color abilities, or anything else that'd keep him from just boosting forward - but we see some legitimate showcase of skill here.
I'm not sure how I feel about Modern Sonic's gameplay on Generations though. His gameplay was sorta repetitive in Unleashed, since most levels relied mostly just on boosting and avoiding things, having little variety to it, and I really enjoyed Colors because it added really good level design, a whole lot more platforming to it, and the Color Abilities, which opens a whole lot of variety to it. Modern Sonic though, will not have that much platforming, and will not have the Color Abilities (unless in Planet Wisp maybe?), so it pretty much counts only on a better level design that has more variety to it.