Long before the artwork in big-deal blockbuster games get turned into polygons or texture maps, it can start as pencil drawings or oil paintings. Dev studios use these pieces as inspiration to help them focus on the worlds they're trying to craft or look at them after the fact to remember where their creative journey started. I snapped pictures of four such pieces last week at E3 because it struck me how quiet and abstract the rendering were when compared to the games they're attached to.
You shouldn't need any clues to figure out the four upcoming games, as each art piece belongs to a game that thousands of people all over the world can't wait to get their hands on. They've all been covered on Kotaku, though, and some of them even netted some coverage during E3. That's probably not that much help. Sorry.
As many have guessed, the games represented by the artwork are Guild Wars 2, The Last of Us, Halo 4 and Dishonored