For instance. good use of arctic tundra planes, jagged and surreal mountain formation. giant scottish-style castles, etc. When you climb a tall mountain, you should get howling blizzards blowing in your face as you traverse slowly through knee-deep snow, you should be greeted by chirping crickets and blacklfies as you trod through melted arctic tundra, there should be lots of dense, short forests, steep, terrifying canyon valleys, mirror-top alpine lakes.. theres no reason you cant take a normally conventional worldspace and make it amazing and atmospheric.
these are the sorts of things I hope to see
http://www.donpaulson.com/AlpineLake.jpg
http://users.snowcrest.net/wb6fzh/alpl5.jpg
http://thundafunda.com/393/images/wallpapers/animals/the-wild-sprit-andes-mountains-argentina-group-of-horses-pictures-wallpapers.jpg
For sense of realism, there will be a need for bare areas, but even with bare areas you can make them exiting to traverse. Imagine being on horseback, ripping across huge, barren glacial casm, with towering, knife edge mountains around you on all sides. Its all about atmosphere, to gain good atmosphere you need to combine both stunning visuals, and a freakishly real sound-scape, with those two things, even barren wastes can be fun to traverse.