Well, the fugue and the prelude style that Bach developed so well may have gone out of style in the mid-18th century, but I personally think that the fugue is one of the greatest formal forms of music even today. That Bach was the master of the fugue is probably not disputed by anyone - no one else's seem to come even close to being as good.
Yes, Bach was a plagiarist. He stole melodies from everywhere. But this was quite common in those days and was not thought ill of as it is today. As Kapelmeister to two particularly musically-inclined bosses, he had to maintain a spectacularly-high output of new music, novelty being the name of the game during the Enlightenment.
There is one of his preludes which caused me some problems when I was studying for my advanced Trinity exams for classical guitar many moons ago. I had it as a piece of lute music. My mother had it as a piece composed for the clavier, and a slightly differently fingered version of it for the harpsichord - played today, of course, on the piano. There was also an arrangement of the same damned melody, in fact the whole fugue, for chamber orchestra. Since I had to attribute the efforts of all involved, I spent several weeks trying to track down who had arranged the piece I had for lute. It was only after I contacted a knowledgeable music librarian in Germany that I found out the truth - Bach had actually done them all himself. Wily, lazy old bastard that he was! I'd have dug him up and done for him myself if I could have, at the time.
I'd hesitate to agree that Bach was more than just one of a bunch of (mostly German) composers and musicians who were early adopters of the new tempering system. He was probably one of the more prominent, but during his own lifetime he wasn't all that well known, or at least, no better known than several others.
But, no matter what his faults were, there was always the fugue. JSB forever, I say!
