My recommendation list is going to be a wild mix of different styles. Basically aynthing in my Games Library that I find visually appealing…
Gibbous - A Cthulu Adventure: While it isn’t my favourite point&click (that price goes to the Deponia Trilogy), it’s by far the most beautiful I’ve played up to now. The attention the devs paid to detail is astounding. The animations are perfect. In other words: A work of art.
Euro Truck Simulator 2: I might be an exception here, but to me the main selling point of this game is the scenery, not the trucks.
Elite: Dangerous: Most of the times this game looks utterly boring. Sometimes however, you catch an exceptional sight. Here’s a screenshot of an eclipse in a binary system, as seen from an icy moon of a gas giant (behind which the primary star is hidden).
Space Engine: Same argument as for Elite. Most of the stuff is boring. Sometimes you find an exceptional sight. Also, Space Engine isn’t really a game, but rather a “beautiful picture generator”, as there is no real gameplay as of yet.
Dwarf Fortress in ASCII mode: The ASCII “graphics” are a work of art on their own. Especially the animations. And the best part: The ASCII version can be downloaded for free, while the (imho less beautiful) graphical version costs money.
Pyre: A mix of Visual Novel and Sports Game. The backgrounds and characters are beautifully drawn.
Beat Hazard: The colours of the effects are stunning.