Production-wise, it's muddy and unclear and the mix can be too quiet for its own good. Your sounds are fine, just that I feel you need some work with the general panning and EQ (which is a difficult subject, I understand) to really make things stand out and feel much sharper.

Getting that out of the way though: arrangement was very nostalgic, handled the source material well and its legacy throughout the Sonic series. It may play safe, but it didn't need to dive too far if staying true to the original's meaning was your decision. Definitely not bad at all!

For the record: I found Green Hills (Sonic 2 GG), Mecha Green Hill (Sonic Chaos) and a hint of the title screen version in Sonic CD. If there were 4 other cameos, I couldn't find them ^_^*