Compared to Street Fighter 2 Turbo for the Super NES, the Genesis version for the VC is totally unnecessary.
The Genesis port of Street Fighter II is basically the same as the Super NES ports; with both Champion Edition and Turbo included. Speed can be adjusted, just like the Super NES port of SFTurbo, and run as fast as you'd expect. All the World Warriors make the cut and, for the most part, control fine. It's the same Street Fighter II experience that you'd get when you're playing the SNES versions. But my personal opinion (and you don't have to agree) is that the Super NES versions are the better bang for your buck because the graphics sport more colors and it just basically looks a lot better on the Nintendo side. Sound effects appear a little off, and voice samples are garbled--almost like shouting Hadoken while gurgling Listerine.
I'm not saying the Genesis version of Street Fighter II is a bad port--just unnecessary considering the fact that Turbo and the original game are already available for download, and are much better choices. The Genesis game is the exact same thing--only weaker and less impressive. If you're looking to play Street Fighter II in its 16-bit glory like the good old days and are at that crossroad about which version to choose, the Super NES port of Turbo is a no-brainer. That said, there's no reason to even consider the Genesis version.