My room is actually very good. 15.5 x 26 and is a dedicated space. Only used for listening to music. And yes, I do feel fortunate to have this space and credit my wife for being very understanding while house shopping 15 years ago.
IMHO, the worst room is usually an open floor plan with very high ceilings. Our living room is an example of that and I gave up trying to get anything to sound good in there.
Oz