Ian Bogost describes what he sees as "proceduralist style" in the "art games" of Jason Rohrer, Jonathan Blow, and Rod Humble in his article "Persuasive Games: The Proceduralist Style" on Gamasutra. Bogost defines the "proceduralist" genre, typified by the work of these particular designers, by their contemplative mode, minimalist design, and conceptually driven structure. In the conclusion, Bogost emphasizes that these characteristics emerged in response to the direction of more mainstream games. What follows is a short excerpt from that section, which I found particularly interesting, but the article is worth reading in its entirety. The comments are worth checking out as well, as readers not only parse Bogost's argument but also grapple with the stigma surrounding art criticism (which appears to be more pronounced within this context).
In artgames of the sort in question, the procedural rhetoric does not argue a position, but rather characterizes an idea. These games say something about how an experience of the world works, how it feels to experience or to be subjected to some sort of situation: marriage, mortality, regret, confusion, whatever.
As a style, proceduralism takes a stand contrary to conventional wisdom in game design. At a time when video games focus on the realistic simulation of experiences, proceduralism offers metaphorical treatments of ideas.
At a time when video games focus on player gratification, proceduralism invites player introspection. At a time when video games focus on facilitating user creativity, proceduralism lays bare the subjective truth of an individual creator.
Whether or not the style has a stable future in its own right, it issues a specific challenge to our conception of our medium from within. And that if nothing else is most certainly a feature of art.