Playable Metal Sonic, Eggman/Robotnik and Honey the Cat I think is worth the investment for StF...and I know it's not the most complex of fighting games out of the three, but at least there's something to be had with those three characters being playable.
I hope that Fighting Vipers comes out at 800 points to be honest and that they retain Pepsiman....all they need to do is make achievements for some of the secret characters as well as a few beating the game with them.