First some comments on the edition: I compared this in a bookshop with other versions available, and by far and away I found this to be the best. The fact that this is a parallel text is a bonus for greek readers. However, the main selling point is the sensible and informative introduction, the useful chronology of Cavafy's life and the notes that don't try and explain the poems' meanings, but give you just enough to get going on making sense of the harder verses for yourself (which is always just as it should be in my view). I also compared the translations of a couple of poems, and plumped for this edition, since there's nothing unnatural or 'un-english' about the syntax or word choices. As the introduction states, Cavafy developed such a distinctive poetic voice that this can't help but come through in translation, and these renderings seem to do him full justice.
The poetry itself came as something of a pleasant surprise. I do have a liking for writers who take historical events and who try to explore them from the inside, from the points of view of those who were (or who may have been) there. Eliot's "Journey of the Magi" is an example of this. Robert Graves and Rudyard Kipling are two writers who did it at length. Cavafy is, I think, the master of them all. Being a Greek Alexandrian his work shows a keen sense of history, in particular an awareness of how important his city was in classical times. Hence his tendency to use his poetry to make sense of what it could have been like to live in classical times. A good example of this is the poem "A Priest at the Serapeum", which explores the complex and ambiguous thoughts of a son, a committed Christian, on the death of his father, a pagan priest at the City's most important temple.
Cavafy is also a great lyric poet. Homoerotic desire fuelled a lot of this work, but not all of it, and in lyrics like the famous "Ithaca" he strikes a universal chord. Regardless of your nationality, age or orientation, there's something in Cavafy that can speak to all of us.
Given that his total poetic output is relatively small, I wouldn't really bother with a selected edition. Get this book and it will last you a lifetime.