During my neverending internet exploits, I came across a free online Sonic game. It's 3D, but it does it extremely well, and
online capable. I've been playing with people all day, it's a blast running around a level with someone else. My only gripes are with the camera, and the amount of controls the game throws at you. I'm fine with just using my left mouse button to run and my right to jump, but some people wanna use the new stuff--there's a taunt, light dash, and ring toss button now.
Nothing has been comprimised, by the way--Tails can still fly, Knuckles can glide. Just check it out.
Get it here. I promise, you'll like it. :o