Some useful stuff on temperament here.

It suggests that the "Well Tempered Clavier" was written not for equal temperament but for a temperament devised by someone called Werkmeister. Werkmeister's temperaments were not equal, but unlike meantone, the compromises involved permitted playing in all keys. It is thought that the notion of different keys having a different character came from such temperaments as, unlike equal temperament, the intervals between successive notes, and especially of the thirds and fifths were not the same in all keys.

I remember some years ago attending a talk on tuning and the speaker had a spinet tuned to quarter comma meantone, a common temperament certainly in the Baroque. Early in her talk she demonstrated the effect of the temperament on different keys by playing a G major chord followed by an Ab major chord. The Gmaj sounded fine. In contrast Ab major sounded horrible - a clashing discord. It was a graphic illustration why meantone only permitted playing in a limited range of keys.