pretty good
those sprites were redrawn Bass sprites right? some of the stances look familiar.
i don't think this was like DBZ at all, they could have very well had their own Super forms just like Sonic and every other chracter in the Sonic series.
but add a little more depth into it next time around. possibly have Sonic as one Mecha and Shadow as the other.
just be sure to make the difference between Mecha Sonic and Metal Sonic clear