(Leopold Stokowski's orchestration of Bach's Toccata and Fugue. Fantasia made this easily the most famous Bach Transcription of all time.)
Sir Thomas Beecham's Messiah got me thinking about my favorite orchestration of a Baroque masterwork. For the moment let's begin by stating the obvious: none of the transcriptions could possibly be improvements on the originals. But these pieces, particularly Bach pieces, are so universal that they could be played by 150 bagpipes and still work just as well. Some transcriptions are very similar. I'll never forget a concert I went to as a teenager featuring Leon Fleischer playing the Bach chaccone on the piano with his left-hand. The arrangement was done by Brahms, and the only major difference was that the piano played an octave lower with some harmonies filled in here and there. But half the audience (myself included) was in tears halfway through the piece. I find it far more effective than the famous two-handed Busoni trascription, which Lisztifies the piece and turns one of the most moving pieces of music in the world into a bit of a slam-bang virtuoso display.
But that doesn't mean that there is anything wrong with departing from the original. Not all of us are Brahms and can meet Bach on his own terms. I've often thought about doing a two-hand piano transcription of the fugue from the c-major sonata for unaccompanied violin. It would probably sound much more like cheap imitation Beethoven than cheap imitation Bach. There are many other ways of transcribing Bach, and nobody has to adhere to the spirit to which Bach intended to make memorable music.
(Some random internet person mooging it up with a synthesizer. The piece is Wachet Auf (Sleepers Awake) from the Cantata no. 140. It's in the style of Wendy Carlos, who caused a near-revolution in the late 60's with her album 'Switched On Bach' which transcribed Bach for the synth in wholly new fashion. One day her style will be back in vogue.)
But for sheer testosterone-laden excitement, nothing beats Ottorino Respighi's transcription of the Passacaglia and Fugue for Organ. It produces some remarkably delicate moments too, but few moments in music are as exciting as brass-pulverizations at the end of the Passacaglia. It's not what Bach had in mind, but it's a totally different kind of greatness by a good composer whose sole skill of genius was for orchestration.