The entire premise of Portal is based on the ability to use 3D rendering technology to create the effect of opening up portals between surfaces. I don't think anyone would argue that Portal is a shallow tech demo. Narbacular Drop maybe was a shallow tech demo, but that same tech-based premise, when used by a masterful game design team, created one of the best video games of all time.
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.
Narbacular Drop maybe was a shallow tech demo, but that same tech-based premise, when used by a masterful game design team, created one of the best video games of all time.
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 ).
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.