Well, creating a timeline concerning the rise and wane of Dylan's considerable talent is easy, but the criticism of his work is a more subtle enterprise. That is the actual analysis, inspection, parsing, interpretation, theorizing of the music and words themselves, and the taking into consideration the external factors --politics, fashion, religious conversions, divorces, age--that inform the creation of the music. Criticism is the x-ray we use to get inside the work and attempt to come up with adequate terms and descriptions as to how Dylan's material works and , perhaps, why it stands out among the throng of other singer-songwriters who hadn't near Dylan's resourcefulness.
Criticism, distinct from the consumer-guide emphasis with reviewing, is an ongoing discussion that seeks less to pass judgement than it does to comprehend large subjects thoroughly by interrogating one aspect of the work at a time. It is, of course, something like a make-work project as well, a means that some of us use to escape the terrifying silence that falls behind all of us at one point or another, that emptiness of space that sends a shudder down your spine when it seems even your thoughts are too loud and echoing off the rafters. Many writers keep writing, turning from mere expression into pure process, and it is with a good many worthy writers where we can look and see where their particular timelines became crowded with product that vacillates crazily between good , bad and awful, rarely matching what critical consensus considered their best material from their best period.
Edward Dorn is said that almost any good poet has written all their best work by the time they reach age 35, with the general output after that time becoming less daunting,daring, spry. Dylan is like this, I suppose, as is Woody Allen, John Ashbery , John Upidke, and Elvis Costello. I'd always thought that it was a hedge against death, that as the hair and teeth fall out , the arthritis escalates its assault on the joints and the memory takes on the consistency of swiss cheese, the writing, one poem after another, one novel after another, one movie, one song, one opera after another, the work somehow forestalls the inevitable darkness that awaits everyone. And criticism comes in again during these late period efforts of less notable content and turns itself into apologetics, where one theorizes about the proverbial canvas and kinds being changed, the brush strokes being bolder and less intricate as established ideas are played through yet again. It seems we're stuck with this crazy cycle ; even critics, great ones and mere carpetbaaggers, want to deny death in some sense and also avoid the idea altogether that they've nothing left to say about another man's words.