As much as the virtual console sucks, the recent genesis/megadrive remakes are quite good actually and they deserve their price tag more than the nintendo games on the VC.
I only got Sonic 1 and Shinobi 3. For both, you can remap the buttons, choose the audio processor, the version (International or Japan) or the 3d rendering. The most interesting are the added gameplay features which you can enable or not. In Sonic 1, you can do the spin dash just as in the following episodes. In Shinobi 3, you get to play with 6 buttons which makes guard and throwing projectiles easier.