At first glance The Witness is a puzzle game, made annoying by the fact that you have to walk everywhere instead of clicking "Next Puzzle". But then you occasionally see things in the environment that are just really pleasing. An example that springs to mind is a bunch of broken metal in a window[0], and some branches on a tree, that line up with the sun (which doesn't move) to cast a shadow of a woman sitting underneath a tree[1].
And there's loads of this stuff. And noticing it doesn't contribute anything at all to the apparent objective of the game (except where it does!), but it adds so much that you just wouldn't get if it were the simple puzzle game that it initially appears to be.
I really like this game.