Witcher 3 is too uneven to look really amazing, especially without mods. In my 130 hours I spent in the game, it was ranging from very pretty to PS3 territories.
I think the best looking PC games are The Division, Ethan Carter and ROTR. Modded GTA V and Doom look and run pretty great as well.
Overall, I still think Uncharted 4 is the most detailed and the best looking game I've ever seen. Some parts are genuinely jaw-dropping and the fact it runs on a glorified toaster is even more impressive. Of course, you can see where some corners have been cut but still.
Horizon: Zero Dawn might top it, though.