You should have a nice, strong center image but the soundstage should also spread across the area where the speakers are located. You should hear sounds from the center point out left and right with instruments hanging in acoustic space.
If you have a well recorded live event, you should hear the venue's space, air and localization of where the instruments(voices) actually are located on stage.
My system throws a wall of sound that extends way past the outer speaker boundaries with a strong center image. Some say I have speakers in the wall that there's no way that can come from 2 speakers.
One other less talked about feature is image height. It should almost go from the ceiling to the floor. This is sometimes refered to as size of the soundstage featuring height and width.
Lastly, a lot has to do with the recording itself. Don't expect orange juice from squeezed prunes!
