Check out these screenshots:

http://www.thehunter.com/pub/images/screenshots/screenshot_001_large.jpg
http://www.thehunter.com/pub/images/screenshots/screenshot_008_large.jpg
http://www.thehunter.com/pub/images/screenshots/screenshot_014_large.jpg
http://www.thehunterwiki.com/wiki/index.php?title=File:TheHunter-2009-09-22-19-52-.jpg
http://www.thehunterwiki.com/wiki/index.php?title=File:TheHunter-2009-09-22-19-55-.jpg
http://www.thehunterwiki.com/wiki/index.php?title=File:Wh1.png
http://www.thehunterwiki.com/wiki/index.php?title=File:SC1.jpeg
http://www.thehunterwiki.com/wiki/index.php?title=File:SC4.jpeg
http://www.thehunterwiki.com/wiki/index.php?title=File:SC2.png

These are from the game called The Hunter (I'm not advertising it, because the game is free). It's an open world simulator and I posted this to show what modern engines can do. Graphics, draw distance, weather effects and environmental sounds create stunning immersion and realism.
Todd Howard said that guys from Bethesda play many other games. I hope that they played it, because in terms of open-world design, it's truly superb.

Which other sandbox games would you like to see as an inspiration for Skyrim design?

Well, they should try out Arma 2 (Chernarus map) and Arma 2: Operation Arrowhead (Takistan map). Maps doesn't "suit" RPG as they are true in scale (little happening compared to Oblivion and what I expect Skyrim to be), but styles could be worth a look. Also have some interesting sound features, tidal waves, sun reaction to season and latitude (latitude needs mod to move island), walking about in forests checking out sounds and (limited) wildlife. But, maybe they already did

I agree, many elements in Arma's world design can be implemented in Skyrim. Just Cause 2 in terms of scope and RDR in terms of wildlife, too. Thanks for your comment

Skyrim will look allot better than the hunter though.... still a cool game.

Some pointless comments have been deleted.

OK, let's put it this way: Talk about any open-world game as you wish, as long as your post can potentially help to improve Skyrim's design. That's what I said in the first place.
So, feel free to express yourself