What is so great about this poem is that it takes five ordinary nouns: coffee, crumb, balcony, sun, and river; and one abstract one: miracle--and weaves them in to a clever, strange sestina.
The poem pulls off the use of such ordinary words by thinking about them in interesting ways--such as loaves, "buttered, by a miracle", the question, "what under the sun", and, "my crumb / my mansion." The strangeness here works well, making it seem as if it were not imposed by the form.
Likewise, focusing on unique imagery:
One foot of the sun /
steadied itself on a long ripple in the river.
helps to draw attention away from the devices necessarily imposed by the form--refocusing instead on compelling lyricism.
What is so great about this poet is that, as well as being brilliantly adept at blank verse, she helped revive forms like the sestina in modern poetry, breathing new intelligence and insight to the constraints of formal poems, inspiring generations of writers to come to consider what prescribed forms can offer in modern poems.