The Vertical is about Quest, Plot, and Narrative, while the Horizontal is about Things, Places, and Characters.
I see two different aspects of this kind of game that make them so interesting as a lens to look at life. Maybe we can call them the Horizontal and the Vertical aspects.
I see the Horizontal as Phenomenology and the Vertical as Teleology.
The main feature of Open-World Games is that they open up the Horizontal aspect by making the Vertical aspect less predetermined. For the player, this is experienced in terms of Freedom.
As described in 📙 After Virtue, Virtue Ethics has a Vertical axis centered around Flourishing and the Common Good. Life may be a kind of playground, but it has structure and directionality.
In games like Morrowind, there is a Main Quest and a strong Vertical dimension, but the player isn't predetermined to follow it. There is a wide variety of Side Quests.
Through 📙 Experiences of Depression, we can see how a collapse of the Vertical can be an existential issue in forms of “manic” depression where salience and action are present but disconnected from larger structures.