A few things.
-Music sounds horrible, not because of the sound quality but it sounds NOTHING like Green Hill. I know SEGA has to pay to use Sonic 1/Sonic 2 music tracks, so it's a shame they were cheap enough not bother paying the licensing fee to play Green Hill. Even a 8-bit remix of Windy Hill or Seaside Hill would have been better. They paid for the fee to use the track in Sonic Mania (and likely other fees to use Sonic 2 zones too), so it screams 'We don't care' the track not having a proper remix in forces.
-Level design looks lazy and nothing like Classic from Generations. Sure, he felt 'off' in Gens but at least the level design still had the 'spirit' of the classic games. Here, it feels like it was thrown together. The strange spring and booster placement shows this quite clearly.
-Visuals look great for both Sonic and the level itself. I had a feeling the Nintendo Direct footage was the Switch build running and this gameplay video proves that; this seems to be running on PC's or PS4/Xbox One. So the level has a high resolution, great coloring and looks great. The fact it 'seemingly' runs at 60 makes it even better.
-Sonic himself and the stage/objects/etc look 'Classic' like, which is great honestly. Love the touch of Green Hill losing it's water and it being covered with sand. Hopeful they can expand the level (if there is an act two) to use the sand in a creative way to make the stage stand out.