This game had amazing potential and you could see that in the entire hour of play.
You start out with four playable racers. Sonic, Tails, Knuckles and Amy Rose. Dr. Robotnik is a visible unlockable character on the select screen because he races you as well. Five racers at a time will scorch across four (yeah four) tracks. Once you come in first on all four tracks, you may play in the fifth and final (yeah final) track. Coming in first here plays the credits and unlocks Robotnik as a playable racer. Each of the first four levels has five hidden Sonic Coins. If you can manage to collect them all and still come in third place or better, you can challenge a secret character. Beating the character unlocks him. Here is who's on what course...
-Resort Island - Metal Sonic (a faster, higher jumping Sonic; can run on water for a limited distance)
-Radical City - Puppet Tails (a faster Tails who has a crazy, no-limit flying ability. You need to pick a height though, he will stay at that height untill you release the button)
-Regal Ruin - Egg Robo (a faster Dr. Robotnik)
-Reactive Factory - Cyber Knuckles (better stats than Knuckles; can run over water for a short distance)
You can also collect emeralds in each course. I won't reveal where they are, but there are seven like in all Sonic games, so some courses have more than one. Once you collect the emerald(s) on a course you must come in first to keep them! I suggest getting them all before unlocking secret characters. Your reward? Why of course, it's Super Sonic. Unlocking the other characters will be a breaze! But you won't really need them and probably can't win with them now that Super Sonic's on the course. Yes, Super Sonic is by far the best character. With better stats, in every stat, than any other character he is virtually unbeatable.
Apart from the great cast of characters and detailed environments, the musical score was AMAZING. It may be the game's best feature. I don't even like techno/dance stuff and I love the game's soundtrack.
The game also features multiplayer, but it's obviously not online so sharing a keyboard gets cramped. I wouldn't recommend buying it due to the severly short gameplay time (I can unlock everything in well less than an hour), but if you have a friend who is willing to let you borrow it or give it to you free (or at least VERY cheap) then take it. Hells yes!