It's definitely up there.

shadow of the colossus is open world, i say skyrim is down-right ugly compared to that game

Well Assassins Creed games are technically open world so i'd have to agree with that, Made me "ooohh Nice!!!" more than any game since the original Far Cry (PC) when you first step outside. (still my biggest WOW moment)

It's certainly the most detailed. Seeing insects and splahes off the water and the like is a joy.

I tend to equate 'beautiful' with lots of pretty colours and trees and flowers and lakes and whatnot, so maybe 'beautiful' wouldn't be the right word for me. But 'stunning', perhaps.

Games like Assassins Creed definitely have better animations (no contest there), but what other open-world game on the market there allows you to enter every house you see, pick up every flower and go to every mountain you see on the screen, except Skyrim? In Assassins Creed, you might see a table with an apple on top of it, but that's merely a decorative prop. In Skyrim you can actually pick the individual food items from a dish in the dining rooms. This is a kind of 'beauty' that only comes with such freedom

I agree with the OP. It is indeed the most beautiful open world game I have ever played. Not the most original though. I think the witcher 2 gets the most beautiful semi open world game evah!

on every platform it is, who would not agree?

The first two games that spring to mind are red dead and skyrim. I love the foggy mountains of skyrim, giving it an edge. HOWEVER, red dead has better weather effects. You don't get blizzards, but you get wind when a storm's brewing. Where is the wind in skyrim???? I hear it, but I never see it. Is my game bugged? Even during blizzards and rainstorms... no wind. What gives?

I would say almost on par with Red Dead Redemption and Far Cry 2. And Fallout 3/New Vegas if we consider even the "atmosphere" -apart from their "technical limits" in this regard.

But as i've said elsewhere Far Cry 2 had the most credible vegetation that i've ever seen in a videogame (e.g. the fire propagation was awesome)

Not really. It's pretty, but that does'nt matter for important stuff.
Personally, I think there are a lot of good looking worlds. Nier, Fallout New Vegas, Bioshock. And, those games actually have a good story and they put the game before the look of it.
Some of the desert skies and desert on FO:NV are beautiful. Nier has a awesome, unique world.

However good it looks, it does not make up for it's many flaws.

They spent far too much time fussing about with pretty landscapes and too few time on the actual game.
I would have much prefered they made a less cosmetically pretty game, and made it properly.
It's not like the place stays pretty all the time, even. The textures break up, rocks textures float above their shape, etc.

Being pretty means nothing when a game is as flawed as Skyrim.

Graphically speaking the game have his limits; we have to understand what the Op really means with "most beautiful" - and even aesthetics can be subjective after all.

Ever since i got a HDMI cable Skyrim has looked amazing. I can hardly understand how i managed to play at all before. Im going to have to agree with the OP.

i agree. But fallout isn't beautiful but it suits its atmosphere

Sorry, the Assassin's Creed series wins this round. I also love the Bioshock/Bioshock 2 worlds for their art deco style. In addition, these games have much better stories, making them even more beautiful.