I feel Xenoblade is the only right answer here, mainly because the game continued to floor you throughout the game, unlike other visually stunning games where it's obvious all the hard work went into making the first few hours of the game as engrossing as possible and the rest of the game kind of became more muted. Xenoblade though, kept on delivering until the very end, I remember finishing the Guar Plains and thinking the rest of the game would never live up to that point and just being floored time and again by each new location.

I think Ico is the other game that impressed me immensely in terms of visual, largely because it showed how great lighting and camera work can make something visually unimpressive look amazing. Wind Waker is also visually stunning though screenshots don't do it justice, you have to watch it in motion to see the detailed work that went into it.