What is the most overlooked consideration?

I agree with @ghdprentice that musicality includes the properties of rhythm & pace and midrange bloom but as I stated, it is an intimately subjective criterion.  I consider timbral accuracy first and foremost, then the ability to reproduce the nuances in tonal and dynamic inflection, including secondary harmonics and ambient decay, as well as image palpability.     I guess these are more specific attributes or subsets of rhythm, pace, and bloom.  

Synergy because the best piece of gear will do anything coupled with the wrong one...

 Once bought...

Adressing the three working dimensions:

Mechanical :   Speakers vibrations resonance controls...(other gear vibration is important too but  secondary compared to speakers)

Electrical :  Wall plug and central panel control of interferences...

                    But mostly overlooked , the necessary well  grounding of dac, amp and preamp...

 Acoustical:  the system/room various parameters control...  Balance between diffusion,reflection,absorbtion and control over these ... What is very overlooked is the power of the Helmholtz resonators by their parameters adjustment and their location to tune and tame  a room...

@jsalerno277 

Agreed, there are other sonic aspects that must be correct as well.

What is the most overlooked consideration?

For over sixty years, starting when I was just a kid, I’ve seen/listened to all kinds of systems, from setups built on spare change to rooms well into six figures. And time and time again, the room—the room!—is the most overlooked element.

I’d never call anyone’s system their “ugly baby”—that’s not my style. But if the room is well-designed or even in somewhat treated ones, achieving audio nirvana doesn’t take much (even if you’re listening to Nirvana).

Dust bunnies and cobwebs in the corners? Those are just the marks of a truly content soul.

+1 @ghdprentice musicality

++1 @jsalerno277 I consider timbral accuracy first and foremost, then the ability to reproduce the nuances in tonal and dynamic inflection ...

Both well said.  I will place timbral accuracy over the top as well.  Sometime these two are not mutually exclusive.  For example, timbre accuracy facilitates how we perceive and segregate different instruments in orchestra / symphony music reproduction, affecting our overall emotional response to a piece.