I think the "classic era aesthetics" are an illusion created by the technological limits of their time and artists that tried to make due the best they could with those limits. (At least to an extent.) We've seen classic Sonic artwork of locations in the Sonic world. There are no checkerboard loops in Junio's Sonic CD animations. The glimpses we get of West Side Island and Angel Island in the Japanese manuals are not geometric shapes. They just look like normal tropical islands in a cartoon sort of style. One only has to flip through the Sonic 1 manual and then the Sonic 2 manual to see a huge difference in artistic direction. Oshima's original Sonic was a 30s style American cartoon. In Sonic 2 Yamaguchi turned Sonic into an anime character. The robots are goofy cartoon animals in Sonic 1. In Sonic 2, they are a bit meaner looking and heaps more detailed in their design. Looking at the game graphics Sonic 1 is very simplistic in terms of level art compared to Sonic 2 which adds way more greebling and effects to the tiles and this continues into Sonic 3 and Chaotix. How realistic was Sonic Adventure with it's giant pinball machines? How about Eggman's "play room" on the Egg Carrier? Speed Highway isn't surreal just because the asphalt texture on the roads is a photograph? Compare the "bricks" of Sonic 3 with those of Sonic 1. They are quite different.