I've noticed several people have asked what version this game is on the Wii. The Wii VC game is the Genesis version. For people's convenience, I will list the differences here:
Genesis - Easier Special Stage. - Can collect multiple Chaos Emeralds in one act. - 16-bit Soundtrack, composed by Jun Senoue (who often composes music of Sonic today.)
Saturn - Special Stage was changed. More challenging, akin to Sonic the Hedgehog 2's special stage. - Superior Graphics. - FMVs were included. - Red-Book Soundtrack, composed by Richard Jacques (who also composed music for Sonic R.) - The disk also doubled as a soundtrack for CD players.