Riley, author of the best study by far of the Beatles' song catalogue (Tell Me Why, 1988), turns now to Bob Dylan--``the most important American rock 'n' roller since Presley''--with impressive, but less consistently persuasive, results. As before, Riley steers clear of biography and simply goes chronologically, album-by-album, song-by-song, through the Dylan oeuvre--including unreleased tracks, bootleg recordings, live concert tapes, and concert films. In fact, unlike most Dylan critics, Riley declines to link the songs to the life, contending (not always convincingly) that Dylan turns his ``intimate trials'' into ``public metaphors''--in contrast to ``self-serving,'' Me- decade types like James Taylor. Throughout, Riley stresses Dylan's humor, the satire implicit in his ``bad'' singing, his manipulations of his persona, and his eclectic roots. There's sharp criticism as well as enthusiasm here: The Times They Are A-Changin' succumbs to ``folkie social preening and black-and-white moralism''; Blonde on Blonde is a ``tour de force of obscurantist rock poetics''; ``I Shall Be Released'' is an ``overpraised and overplayed potboiler.'' Riley applauds Dylan's return to ``roots'' in his work with The Band and his country-ish albums but is pretty much appalled by the ``stringent and pious'' born-again albums. And, in contrast to many hard-core Dylan-ites, Riley finds little evidence of a revitalized Dylan once his ``slide'' begins circa 1978. Not everyone will buy Riley's attempt to view Dylan's weaknesses--the clichÇs, the slurred diction, etc.--as ``postmodernist.'' His dense, imagistic evocations of the songs occasionally become precious or strained. (`` `Idiot Wind' is an emotional soapbox as fearsome and cutting as any of the cutlery that flies in Edward Albee's Who's Afraid of Virginia Woolf?'') But, with full attention given to Dylan as performer and writer, to cover versions and disciples (Springsteen, Neil Young), and even to other Dylan-commentators, this is an essential book for Dylanologists: comprehensive, knowing, challenging.