The HN2 artstyle in SN can look good in a quite a few places, but I feel like it's very flawed in other places. Here is how I think it could be improved.
Better Texturing
Textures matter a lot, and having more older outdated textures is very noticeable, especially when mixed with the new textures. This is very noticeable on maps like The Amusement Park, which have a lot of clashing textures. My suggestion for this is use textures that are exclusive to one artstyle, instead of mixing them.
Consistent Artstyle for Assets
Making sure assets are all one consistent artstyle is very important. Clashing assets are very noticeable and can lead the player to feel confused as to what the game is going for in terms of artstyle. If possible, custom assets should be made for things like the teleporter, so that artstyles don't have to be mixed.
I added some images of examples of clashing assets and textures, so its more clear what I mean.