I still play it. I own the GC version, and the PC version. Both are just as awesome.
For people that dont know it, It's a 3D sonic platformer with 6 playable characters with each their own stages. The characters are Sonic, Tails, Knuckles, Amy, Fat-assed Big, and E-102. They all have different playing styles, and are all lots of fun. Well, except big's gameplay. He sucks big time.
Sonic and Tails have fast gameplay with loops, obstacles, and are so much fun. Knuckles is treasure hunting, which is more fun then it sounds really. And Amy is stealth-based action.
Big and E102 play a lot different from the other ones. Big's gameplay is fishing for his frog, Froggy. It'll get pretty boring after a few stages, and not way as fun as the rest of the stages. E-102 is platform shooting, which is pretty fun though.
You can get this game off Amazon, or eBay, and in some shops, if you're lucky. You could download the demo somewhere too. I got it from a secret place. Seeeeeeeeeeecret. So i'm not telling.