Like Teuchter2 I was initially underwhelmed by the final step as I saw an obvious letter from the author's name creating a thematic location, in an appropriate way, but crossing grid lines (unlike destination and author). It felt like a real let-down - but the response on this thread led me to re-read the preamble and I eventually saw the light.
Having struggled manfully on through the cold-solving, (miraculously entering only one answer in the wrong place), I'd eventually reached a stage where I could check initial clue letters. Lo and behold, I found a coherent message which helped complete the grid. But that last step nearly tripped me up.
As it is, I'd have to say this is as perfect a crossword as you could wish for, and the mind boggles as to how Shackleton constructed it. The highlight of my Listener year so far.