On the question of what sound design in cinema actually consists of and why it receives so little critical attention.

Sound design encompasses: dialogue recording and editing, sound effects (both recorded and designed), Foley (the recreation of sounds in a studio setting), ambient sound, music, and the mix that combines all of these into the final track.

Each of these is a creative discipline with its own vocabulary and history. Walter Murch, who is both an editor and a sound designer, has written and spoken extensively about the relationship between sound and image and described the sound design of Apocalypse Now as a collaboration between the reality of location sound and the abstraction of synthesized sound that was politically specific: the helicopter blades that transform into the ceiling fan, the electric guitar that bleeds into combat.

The reason sound design receives less critical attention than cinematography is partly perceptual: most viewers can describe what a shot looks like more easily than they can describe what a shot sounds like. Sound that works is often invisible precisely because it's doing its job of creating a world rather than calling attention to its construction.

The practical argument for paying attention to sound design: once you hear what Ben Burtt did with the audio in Star Wars, or what Gary Rydstrom did in Saving Private Ryan, you cannot watch those films the same way again.