The Sonic 2 beta was released on the internet, and it became the center of some attention. It revealed that Tails may have been meant to be the guardian of the Master Emerald, and shows the time travel element in Sonic CD was planned for some time. Gameplay wise, the beta shows it is a beta. On some levels, Tails runs straight ahead. Tails will not die completely, because when he hits the bottom of the screen, he dies and bounces again. Some levels are not finished, and you fall to your death immeadiately, like Genocide City (nice name, huh?).  A few sprite rips have been made from the few sprites in the game, as most of the enemies are not made. here is what there is.

More detailed info on this and other Sonic games is available at the Sonic Stuff Research Group