Breja: I don't know... The Trine games are gorgeous. Chains of Satinav was beautiful, very "painting-like". Apotheon is also a strong contender.
I have to agree about Trine 1&2 for sure. I'm not fond of platformers and not a big art fan either per se, but looking at the screenshots of Trine alone got me interested in it as it looked graphically beautiful. Seeing the smooth fluid animation and other dynamics made an impression on me so I picked it up on sale eventually and it was one of the first platformers I played in years and I actually enjoyed it enough to get the 2nd game and play it through also.
I have Chains of Satinav and had it installed for some beta testing briefly but didn't really get a chance to play it so can't comment on that. Dunno the other game at all.
Starkrun: I felt the burn on that :)
For my money no game has ever given me that "OMG WOW" feeling like first steeping out in Skyrim... seeing ruins in the distance and being able to walk to them...
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Out of these, I have to say Skyrim, still takes my breath away!
Aside from Witcher 3, Skyrim was the previous big amazing game I played before that, and it blew me away also, not to the same degree as Witcher 3 but nonetheless I was very impressed much in the same way it sounds like you were. The beginning sequence in the opening town (Helgen? I forget the name) was pretty wicked. Skyrim was an amazing game, I put over 600 hours into it.