Nice video! The entrance to the mysterious forest (with the owl) is a fair bit different in appearance actually. Kanalet castle, as well as the visual differences, has a functional change as it now has a ledge that can be jumped down on the roof where there wasn't one before. In Mabe village there is a height difference with a cliff edge to the left of the flying rooster that wasn't there originally. It makes sense thinking about it as in the original there are "implied" slopes where cliff edges just stop, but now we're in actual 3D they have to actually work those out properly. In appearance the underground section with the goombas is more cave-like now with less bricks.
I literally can't stop myself from poring over every detail
I think I might start another play through of DX on 3DS tonight