While looking through many threads on mixing, I ran accross this one on the reaper forum. It has more info on the reasons for why mixes sound terrible and how to learn how to fix it.
This is not a casual read but worth th time.
http://forum.cockos.com/showthread.php?t=29283

it was posted several years ago but even though I have only read the first 3 pages, I've seen a different POV to sound.
Hope some here enjoy, Wyndham