Sonic GT uses the modern designs for the characters but gameplay wise it's basically Utopia but fleshed out with multiple levels and playable characters.
This would be my recommendation. Of all the games of this style, Sonic GT felt the most fleshed out and finished. It also has a full game coming to Steam without the Sonic IP under the name Rollin' Rascal. Also note that while Sonic GT uses modern character designs, the zones themselves are mainly from classic-style games (like Hill Top Zone and Studopolis Zone).
