I also see that Heroes is the closest to Classic Sonic we've gotten since Adventure (two acts levels, the Chaotix, Metal Sonic back from CD and a colourful art design that ditches realism although SA1 had some Saturn-esque levels as well).
I'm still sad that Neo Metal Sonic didn't get a proper boss fight. He should've been the final boss before you got all 7 Chaos Emeralds...
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He looks a bit like one you'd see in the comics.
The Advance series was nice with having a final boss before the Chaos Emeralds like in Sonic 3&K, I'm wondering why they didn't stick to that formula.