For a HUD level this is quite enjoyable, and a major improvement over SRB2 oak, thanks to not having that dragged-out intro and a more simple way of organizing where all the levels are. The zone HUDS are fun to explore, especially finding the "Legacy" versions of THZ2 and ERZ3.
Personally I hope for more hidden Legacy maps, even if the differences in some maps (GFZ2 and CEZ2 especially) between 2.0 and 2.1 were minor, some of them had stuff that weren't present in 2.1's versions of the same maps.
One idea I have would be to label the doors leading into to the seven different Zones (such as placing a "1" on Green Flower Zone's door, a 2 on Techno Hill Zone's Door, etc). There could also be signs in front of the Old/Legacy Act entrances that have a small "Old" or "Legacy" sign above them, and signs next to each of the buttons in the Special Stage room, showing which SS number it is.