The Orchestra of the Age of Enlightenment performed last night two Beethoven symphonies, Nos. 2 and 3, with period instruments. It was incredible to hear tones so infused with color just by virtue of the acoustics of the instruments. The vulnerability of every instrumental voice went from the extreme wit of the Second Symphony to the naked sadness of the Funeral March in the Third without histrionics, without heavy-handed "interpretation." I felt I was hearing these works for the first time--certainly I felt as if I understood them for the first time.
I don't think I'll ever again go hear these works played with modern instruments.
To give a concrete example of the difference: The French horns are natural horns that produce natural overtones of their fundamental; all other tones require manipulation that give a distinct edge to the sound. The chromatic harmonies that sound so lush in modern orchestras sound truly other-worldly. The strings take their cues from these colorful tone events and the dialogue between winds and strings is off and running.
Go hear them if you can.