Games that allow you to take your time and soak in the atmosphere. The game doesn't necessarily need to lack tight/forced progression, but in some way, it needs to give you the space to allow the world to encourage you to stop and let the ludo-verisimilitude wash over you. Essentially; a tour or travel guide, with lots of sights and characters to peruse and chill with.

Behold -- the pinnacle of the medium.