I have heard a number of rooms built from the ground up as audio rooms with full blown complete room treatment. Even with such rooms, subjective impression of the rooms vary greatly. Most of such rooms were, to me, disappointing—too dry and analytical sounding with bleached out harmonics.
The best was a $250,000 room designed by an acoustic architect. That room did not look like it was treated because most treatment was hidden behind the wall coverings, including the truly giant bass traps in all four corners. The front wall had a very large convex wood diffusor that looked like room decoration, not treatment. But, even this room, which I liked, got mixed reviews. Two of my friends did not like the sound and both are audio professionals. So much of good sound IS subjective.