"The room can totally wreck, or make, a system"

My reference recordings are of acoustic instruments in reverberant space… mostly churches… The first distortion is… microphone selection… 

Not every reverberant space created equal… indeed listening seat… 

Room treatment for speakers is a science and black art…often overdone in those sterile audiophile rooms… don’t get me started by the tank trap forest of amplifiers blocking the TT on a massive rack planted between the speakers….

Don’t neglect diffusion… my favorite are from Arnold at Core Audio Designs… 

I think the title to this thread overstates the issue.  Obviously the room is very important, but it's only a make or break situation if the listener makes seriously unwise choices in loudspeakers.  It involves trade-offs.  If you want full range and loud you will need to utilize acoustical treatments.  If you only listen at moderate levels and you're willing to sacrifice some deep bass, then you'll need less treatments, if any.  Additionally, if you set up a true near field arrangement you can greatly reduce the need for acoustic treatments.  Plus, there are loudspeakers that are actually designed to control and/or reduce room interactions.  Gradient, Snell, Klipsch, Kii, Lyngdorf and others have some interesting designs.  It's more subtle than the thread title indicates.

@onhwy61 your post is certainly true and reasonable. My experience mirrors what you stated. I have had massively to minimally treated rooms throughout the decades. I managed to get all the systems to sound very engaging and enjoyable. Natural wool rug in front of the speakers, more nearfield listening combined with speakers that work well with aggressive toe-in minimizing the room’s impact. Getting acoustic treatments right in a given room can be difficult. One of my highly treated rooms would always sound flat and a tad dull. I learned to use more diffusion and thicker broad spectrum absorption panels to avoid that result.

Furniture combined with book cases and such can certainly help acoustics if well thought out. Some of my listening spaces were in a shared living room making the use of acoustic treatments near impossible! 🙁.

Finally, I have a good audio friend that paid one of the acoustic companies mentioned in this thread many thousands to treat his room. He ended up having them remove most of it in the end. He felt the system lost life and vibrancy. I suppose some of this can be subjective in terms of sonic result. It seems everything in audio including acoustic panel types, placement and number, is also subjective.  Nevertheless, if at all possible acoustic room treatments should be employed, but realize it takes time and effort to do it your liking and preference.  
 

One last point. Many of these acoustic companies will offer to study your room and come up with 2 or 3 price options. I notice these plans all but wallpaper walls and ceiling with a great number of panels. I question this approach. Start slow and test with a few treatments and go in steps! 

"Research proved that in a live musical environment, approximately 30% of what we hear is direct sound while 70% is reflected from walls, ceilings and floors and only reaches our ears a few milliseconds after the direct sound. The human brain uses direct sound for identification and to calculate location, but uses reflected sound to determine musicality and spaciousness, as well as direction."

Right — and this is why a deadened room sounds "weird." 

I appreciate the pushback on the way I phrased the OP. I think it is possible to have good rooms if mid or nearfield listening is possible. That said, the space I was setting up in was going to be near to midfield and it needed help. 

At first, I way over treated it. I got a lot of panels for free from someone local -- bass traps, absorbers of different kinds, a couple diffusers. Put too much in and took a lot out — but not the bass traps nor the absorbers on my 6.5ft ceiling. Things were not right so I got a bunch of diffusers and they did the trick.