A programmer can make a videogame, but a function alone doesn't sell. For as long as videogames have been marketed there's been a concious effort to make them visually stand out, either promotionally or in-game, so long as the engine could handle it.
Dump artwork, promotional renders, adverts, posters, sprites, even in-game screenshots if you're pushing it; whatever you deem made the game cool. With every game trying to find their own visual niche and themselves being a little time capsule for their technology and the zeitgeist of their devs, there should be plenty to cover.
For instance I've always liked the uncanny look of early 3D renders, and believe the technology lost its edge when CGI got standardized and overdeveloped. On traditional artwork, Roger Dean's cover art on Psygnosis games is fantastic. Don't know how they managed to land the job on him but I'm glad they did. A master of the canvas, disingenuous cover art aside.