This is EASILY my favourite of the "adventure" style games and close to being my perfect Sonic game in general.

Story is exactly what I want from Sonic, simple and unintrusive but with enough character to it to stay entertained.
Soundtrack is non-stop banger after banger after banger. (Seaside Hill is the best first level music in the series)
Characters all play the same with their own little twists which is the best formula imo.
Level themes and design is great and creative.

ONLY downside would how slippy the controls get but if this game ever got remade, it'd be hard to top it.