I belive that feedback acts like a kind of twisted tone control.

For example, a moderately good discrete transistor amplifier with an OK but not brilliant open loop frequency response, say 30Hz- 8kHz -3dB, and a moderate amount of low order distortion's (about 3% at medium-ish output) sound will go through a whole range of sound qualities as the feedback is increased from none to say, 40dBs.

This is how I would predict the sound of the moderately good amplifier to change as feedback is increased

none: cold and rather hard sound with hiss and powersupply buzz, but very clear

3-7dBs: neutral not warm or cold sound, less hardness and noise

8-16dBs: starting to sound warmer and sweeter with slight emphasis on frequency extremes, slight mushing of fine detail

17-25dBs: starting to sound a bit oppressive clingy warmth with a slight feeling of grungyness, noise and hardness no longer obvious

>25dbs: Shut in closed tizzy tight sound, a bit like a "transistor amplifer".

The changing sound described above is initially the effect of the interplay between reducing low order distortions and shifting phase and frequency responses within the audio band as the feedback increases.