Not long ago, I attended a Wagner Society of New York seminar on The Flying Dutchman. As part of the presentation, one of the speakers played an unrecognizeable (to me) selection from Rienzi and followed it up with a famous passage from Dutchman. Then, he opined that the leap in development from Rienzi to Dutchman was as significant a leap as could be found in Classical Music.
My first reaction is that one could juxtapose a prosaic passage from Rienzi with a more stirring one from the same opera, and present a similar contrast. My second reaction is that there's a certain amount of 'choir-preaching' involved in the assertion. Essentially all of the assembled are Wagner fans, and doubtless we'd like to believe that "meteoric development" is one superlative that we'll happily add to all of the other superlatives surrounding Wagner.
But surely there are other examples of amazing artistic development, opus-over-opus. There are a couple that immediately sprung to my mind, but I'll keep 'em to myself, for now. (Want to leave some latitude for discussion...)
So- I invite you- contibute your own examples of the "Great Leap Forward!"