Thinking about it more, Green Hill Paradise really reminds me of the Playground mode in GRIP.
https://www.youtube.com/watch?v=2tQf724gNv4
There's definitely a lot to nitpick about it. The camera during the boost mode is pulled out way too far. Rings and enemies are too small. I don't like that you keep so much momentum after a homing attack. Doing an air dash without a homing target feels weak to the point of being worthless. I get hung up on stuff a lot when I'm rolling down a hill to charge my boost.
The level also reminds me of something StreakThunderstorm on Sonic Retro made many years ago for BlitzSonic.
This is the only video I can find of it on Youtube.
I think what separates Green Hill Paradise from the GRIP video I linked above is that with Green Hill Paradise, they're obviously trying to bring the Sonic & Knuckles level design sensibilities in to 3D, which is what Streak tried to do with his Green Hill Zone map. But with the way you have to design an environment like that, it just becomes sort of a maze. You end up spending a lot of time staring at valley walls and not really seeing things from a bigger picture.
It's intricately designed, sure, but it feels very easy to get lost and it kind of lacks direction. GHP tries to get around this by sticking "GO HERE!!" arrows everywhere, but I dunno if that's really the best idea.
Comparatively, GRIP is a lot easier to get around because it's very easy to stay oriented. You have a clear view of all major distant landmarks.
And it's not really helped by the fact that enemies just seem to be placed kind of at random. They roam around a lot, and sometimes they're just straight up placed in your way or in what feels kind weird, out of the way places.
That being said I don't think it's bad. It's an interesting experiment. Exploring it is fun. But I don't think a whole game like this would work out too well.