Class-D amplifier of present vs Class-A of the past
Other than unmeasurable parameters only detectable by audiophools, a good class D amplifier can produce the same ultimate sound to a human observer given the same source signal and same speakers as any other good audio amplifier.

The main difference is that class D amplifiers are much more efficient.  With modern electronic components, they can now be cheaper because the additional electronic parts don't cost as much as the mechanical parts to deal with and get rid of the heat in other types of amplifiers.  For battery operated equipment, the efficiency itself is also a important advantage.