Lots of other synth albums are technology demos, collections of cool sounds. Switched On Bach stands out because Carlos adapted Bach for the medium of the Moog synth, clearly understanding the compositions' underlying gestures, and ensured that those gestures all come through. In some cases, they come through more clearly than on the original instrumentation, especially bass lines where the synth speaks more clearly than acoustic instruments can.
Such details in another performer's hands could be distracting, messing up the relationship between foreground and background elements and drawing attention to the wrong things -- but Carlos's arrangement and performance are exquisitely balanced. This could only have been achieved by someone with a deep and sophisticated understanding of the source material, combined with incredible patience to wrestle with difficult and immature technology until the recordings were perfected.