In that case I wouldn't call it a game, but more of a tech demo or an interactive experience.
In that case I wouldn't call it a game, but more of a tech demo or an interactive experience.
Cramming more graphic textures or perfecting water algorithms might be secondary (or tertiary) to the game, but they can still influence the gameplay directly. Take Team Fortress 2, where a lot of care was put into making each character class have a distinctive silhouette, so at a glance you can see who everyone is from a distance or from different angles - this isn't what most people talk about when they discuss "graphics," but it is the element of graphics that matters most.
Likewise, the entire premise of Minecraft depends purely on the simplicity of a voxel-based world - a technique for defining a procedurally-generatable, deformable landscape. Maybe Minecraft is only a tech demo or an interactive experience, but... it's a damned successful one.
What has the story and design of Portal to do with graphics? Nothing, because story and design are independent of it. Would Portal be an equally great game if done with the engine used in Narbacular Drop, but with the same design and story. Yes, again graphics has nothing to do with story and design.
So to reiterate. What made Portal great has nothing to do with how many pixels you fit on the screen or how many shadows you can render. What made Portal great was story, design and the tech( portals ).
Sure, the number of pixels you fit or the lighting effects are not key to Portal being a good game- but being 3D certainly is.
I also recall that you could replace the peons' wood-chopping sounds with fart noises, which was hilarious for almost 30 whole minutes.