Sonic R is a fun little game. The issue is that it's insanely short and has a total of five stages. There's no game balance for multiplayer either, since the characters are either amazing or suck.
Maybe if it had, like, 12-20 stages like most other racing games, it could have gone farther, but as it stands, it's an interesting game that's fun for 2-3 hours, and then goes back in my stack of CDs for another few years.
The Sonic series went kaput with Sonic Heroes, personally. They tried to "reinvent" the series by removing the stuff in the 3D games that actually worked and adding stuff that breaks the flow and ruins the game, like multi-hit enemies and that god-awful flight formation.