Xenoblade, followed by Castlevania: Lords of Shadow.
Ni No Kuni was also really pretty, but I think it had a lot of potential that went unfulfilled. If they could have made giant expansive -explorable- environments like Xenoblade had, but with the Ghibli artstyle... Ohhh, woe be unto anyone who could call it "kiddy" after that...
And thus, did SquareEnix churn out Crisis Core, further propagating the downfall of the industry. -- Gamer's Bible, Book of the 2nd Crash, Chapter 2, Verse 3
Final Fantasy X and Valkyria Chronicles, can't split them. So, so beautiful, but in such different styles. Coincidentally, they are my two favourite games of the last two generations. Ni No Kuni is also absolutely beautiful, but it's art style is similar to VC, and VC did it first, so that gives it the edge IMO.
As far as nostalgia goes, when Kingdom Hearts & kingdom Hearts 2 came out it blew my mind with those CGI openings and the graphics where pretty awesome for it's time
PoP 2008 is the most beautiful game artistically that I've played
A maxed out Witcher 2 and BF3 are both technically stunning, however Skyrim with an ENB and a gazillion texture mods can look damn near perfect and although GTA4 is a fairly old game, with the right mods it can be hard to determine some of the screenshots made from real life.