In terms of art direction. I was thinking which I would place on top.

My pick would be Okami. It's almost like a painting in motion, although looking back on it without rose tinted glasses I wish the terrain was a bit less polygonal, and the colors were a little more vibrant, but I still think it is phenomenal.

HuniePop.

Hard to be objective, as I remember and can compare the impact at the time better than the actual quality.

But still, I'd say Stalker.

The new Zelda BotW looks so beautiful.

No Man's Sky trailer.

I don't know... The Trine games are gorgeous. Chains of Satinav was beautiful, very "painting-like". Apotheon is also a strong contender.

zelda windwaker a cartoon in motion

mirror's edge stunning in its starkness

I'll second Trine 1 and 2, and I'll add the Amanita games.

Also, OK graphics + amazing scenery make Brothers: A Tale of Two Sons such a beautiful game...

And in a completely different style, the combination of graphics + soundtrack (not the one in the trailer!) of Eufloria.

Botanicula- yes. But not Machinarium. It was way too much brown and grey and grey and brown and it was just very dull looking to me.

Hmm...
The art direction of Final Fantasy VIII, I like very much.
Shadow of the Colossus is fantastic, in the lonely atmosphere genre...
I think the latest really impressive looking game I hold dear is Dragon Quest VIII... It pushed the Playstation 2 so far in Toriyama style it really came to life.

EDIT : I forgot, Zelda, The Wind Waker!

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I would not say "ever" since that kind of term typically ends up being an overstatement, but there are some I've played in recent years that do very much stand out:

Ori and the Blind Forest - One of the most gorgeous games out there
Rayman Origins - The game's extremely whimsical playfulness is perfectly displayed in its art style.
The Night of the Rabbit - A beautiful adventure romp

You may notice a trend there. IMO, well done 2D art will always look and age better than 3D.

Very difficult question to answer, but those who know me will guess I will say The Witcher (1 that is, as I was staggered by the graphics from the opening scene.)

I also love Dragon Age Origins.

omg okami on the wii is one of my favorite games ever and one that i think is visually stunning. i replay it at least once a year.

It looks old today, but Red Dead Redemption. Damn, it was like Sergio Leone would still be alive.