“Schubert’s ‘Unfinished’ Symphony, Coleridge’s ‘Kubla Khan,’ Dickens’s ‘Mystery of Edwin Drood’: These are all works of art left incomplete by their creators, works that have invited speculation and fantasy for years. Those with a love for American popular music would immediately add ‘Smile’ — the legendary, lost Beach Boys album, begun and abandoned in the mid-1960s — to this list. … So what are we to think of ‘Brian Wilson Presents Smile,’ a new CD released yesterday?”