Actor-Inspired Element: Bach tended to work with the same musicians a lot because they, like him, had the same employers, and you can tell which ones he especially admired, because a cantata will show up with e.g. a juicy trombone part. He wrote some of the most florid and difficult trumpet parts of the era, chiefly because he enjoyed for many years the services of one Gottfried Reiche, perhaps the greatest virtuoso practitioner of the natural trumpet. And he loved incorporating unusual and novel instruments into his works, such as the oboe da caccia, a tenor oboe made of metal and curved in the shape of a hunting horn.
Awesome Music: Too many examples to list, but just one would be the Chaconne for solo violin. The other works for solo violin are all excellent, but the Chaconne (which is just the fifth and last movement of Partita No 2) is notably longer than any of the other movements, and packs an epic, symphony-sized amount of musical information into just about ten minutes. It's been transcribed for numerous other instruments (Segovia did it on guitar), it's one of the ultimate challenges for any violinist, and players as well as composers have been marvelling at it for centuries:
Johannes Brahms: On one stave, for a small instrument, the man writes a whole world of the deepest thoughts and most powerful feelings. If I imagined that I could have created, even conceived the piece, I am quite certain that the excess of excitement and earth-shattering experience would have driven me out of my mind.
Cowboy BeBop at His Computer: At least two recordings of the Third Brandenburg Concerto supposedly consist of the "First and Second" movements. As most fans know, Bach only wrote First and Third movements (and a placeholder cadenza to stand in for the Second; it is believed that the musicians were supposed to improvise something leading up to it), and the Third Movement is definitely in the style of a Third, not a Second. No prizes for guessing what the so-called "Second Movement" in these recordings actually is.
Critical Dissonance: Bach scholars tend to rate the cantatas and Passions as his greatest work; non-scholars and fans often prefer the instrumental music, such as the Goldberg Variations, The Well-Tempered Clavier, the suites for solo violin and solo cello, etc. This probably has something to do with the fact that the sacred vocal works are all sung in German.
Descended Creator: The first movement of the fifth Brandenburg Concerto turns into a lengthy and highly virtuosic solo for the harpsichord, which would have been played by Bach himself.
Genre Adultery: J.S. Bach, the composer most associated with sacred music, writes a mini-drama in cantata form about a sassy girl addicted to coffee.