I think it goes beyond simply just having the Sonic ingredients to it. It also needs to be baked properly too.

When I play a game like Sonic Heroes or Sonic 3, it feels like a Sonic game to me because all the elements work together to give a special kind of nostalgic and fun flavor with the music, the atmosphere, the animations, the attitude, etc.

Admittedly one of the things about Frontiers that's somewhat not settling right with me, is that the attitude and everything hasn't really come out yet. The island and mood feels cold and isolated, and it doesn't really feel like the animation and style really utilize Sonic's personality and capabilities to its full potential. It feels a bit mechanical so far, and while it does look fun to play, hasn't really made me feel that charm I felt with other Sonic games just by looking at them yet.