.....This particular BC is more or less a harpsichord concerto....
....and I think the cadenza to the 1st movement basically originated the piano concerto cadenza as we know it, and perhaps was the main thing that opened the whole door to the possibility of keyboard performance as a spectacular public phenomenon. I 'hear' all that every time I hear that cadenza, and it makes it one of the most moving passages for me in all of music. When I hear it, I'm not just hearing the music; I'm hearing its historical significance and how it has enabled keyboard music to become this thing that has so enriched my life.
I've sometimes imagined how it might have been for the original audience at the very first performance, whenever and wherever that might have been. Perhaps some members with more knowledge of this history might chime in and say what are the chances that this might have been so: I imagine them hearing the keyboard player start the cadenza, and assuming that it would be just a brief interlude before the orchestra comes back in, because after all the keyboard player is just sort of a back-up continuo -- but wait a minute, he's doing a little more.........wait a minute, there's still more ......omigod, he's going into this whole thing......WOW!
i.e. that the whole idea of this extended elaborate spectacular thing by the keyboard player was a total surprise, fairly mind-blowing, and a whole new world. THAT'S what I feel transported back to every time I hear it. And when I hear the opening of the piece -- or even when I see a reasonable facsimile, like Joel's
(and it was a darn good facsimile!) -- I'm put into in a state of reverent anticipation of what is to come.