Beautiful in what sense?
I found Skyrim's familiar terrain to be beautiful. Though I never could say the same about Solstheim in the Bloodmoon expansion.
Personally I thought Oblivion was quite scenic. It was typical generic fantasy and it did so with gusto.
Morrowind though? It was beautiful to me even with it's graphics holding it back. It was strange, sensical and beautiful. Seeing it remade with modern graphics would be amazing. Though I would be kind of pissed that BGS did that instead of a new game. I wonder if a different dev using Morrowind and it's source code could remake it with modern graphics while BGS made the next TES game? Then again there are mods that make Morrowind pretty damned beautiful.
Imo, despte it's age, Morrowind takes the cake. And really, we only saw Vvardenfell and a small part of the inner city of Mournhold.
Some fan art for morrowind really brings it home for me.
http://i.imgur.com/gESGK.jpg
http://fc03.deviantart.net/fs71/i/2010/261/f/e/silt_strider_by_monartt-d2yydgk.jpg
http://i.imgur.com/Masvh.jpg
http://fc06.deviantart.net/fs15/i/2007/087/a/5/Morrowind_by_Demi_urgic.jpg
You could also browse the favorites of my profile in my sig on Deviant Art for some really nice ones.