I don't really understand the difference...

Adventure has story bits between the levels, with dialogue.

Classic is just the levels themselves, similar in style to the original Sonic games.

The levels being played are the same.

It was originally planned for there to be hub worlds in between stages in Adventure Mode, whereas Classic would skip all that and jump straight to the action. Due to time constraints, the hub worlds wound up getting axed, so literally the only difference is that cutscenes play in one and don't in the other.

No idea if they'll be patched in alongside the extra two characters to expand Adventure Mode any, or if that's your lot.

Interesting!

Thanks for sharing that info ShadowHog. ^_^

Thanks!