One thing that caught my attention in the prelude was the final cadence. It seemed immensely satisfying when it was finally resolved with a major I chord (Bach used a Piccardy third). Upon examining the score, I realized why - in the last four measures of the piece, a minor 4 chord in second inversion is sustained for nine beats. It is only on the fourth beat of the pen-ultimate measure that the dominant occurs, and in the final measure, Bach holds of resolving all of the voices until beat three. The overall effect is one of great tension - the four chord is pounded into the listener's head for a long time, and so the final resolution seems like a huge release.
I felt much more interested in this piece than the Vivaldi. There were many more voices, and, simply put, a lot more notes. The harmonic rhythm was also faster and the progression seemed more complex - Bach wanders pretty far from tonic at times.