Translation is a difficult task, and I hesitate to rate them harshly. But in this case, there are several better translations already available (contrary to what the goodreads entry says, this edition was not
originally published in 1979; the entries for the differing Cavafy translations seem all mixed together) so it strikes me as both pointless and hubristic to produce another at all, much less pronounce it "an extraordinary literary event".
Mendelsohn entirely loses the sensuality that characterizes Cavafy's poetic style. He loses much of the ease of tone as well, producing stiff and somewhat guarded entries. To be just, Mendelsohn is not himself a poet as far as I can determine, but since it was his choice to undertake this endeavor I don't see that as much of an excuse.
Compare, for example, Edmund Keeley's translation of "Body, Remember":Body, remember not only how much you were loved,
not only the beds you lay on,
but also those desires that glowed openly
in eyes that looked at you, trembled for you
with Mendelsohn's "Remember, Body":Body, remember not just how much you were loved,
not just the beds where you have lain,
But also those longings that so openly
glistened for you in eyes
To my mind, the later adds nothing in meaning and is slightly inferior in style. Also, why shift the titles? If there is no debate as to word meaning this serves no purpose and makes it harder to look up poems.
Keeley's is a very competent translation. If you can find it, my recommended translation
is the older one by Rae Dalven, The Complete Poems of Cavafy: Expanded Edition, with bonus introduction by Auden. Both Dalven and Auden really seem to "get" Cavafy in a way that Mendelsohn fails to.