Coming around a corner and finding an awesome, beautiful waterfall or a cool bridge to cross or an intimidating looking ancient ruin.
Seeing the entire landscape in 3D before you even go anywhere is going to ruin a LOT of that for us.
For example, if you start the game and want to go to Solitude, so you look at the map, you will be able to see, "OK I will head north from here, pass that giant gray building, cross a stream on that bridge that I see, go through what appears to be a small settlement with four buildings, cross that field, go to the left of that old Dwemer ruin, and then go around the edge of that lake and I'll be there."
Then when you are wandering up that way, you will see everything that you just saw, and none of it will be surprising or unique at all, because you just looked at exactly what you are going to encounter on your way there.
It's much better if you can only see maybe a road, or a body of water, so you can still tell which way you are going but it doesn't spoil everything for you.