I don't envy Gardner Dozois his task of selecting the thirty-six stories in this book from 20 years of his Best of the Year collections--which in themselves required painful decisions to exclude many first-rate stories. I am glad he put himself through it, though. These are the stories that made the greatest impression on him as a reader--a reader with an educated palate earned through decades of fine reading.
My favorites:
Pat Cadigan's "Roadside Rescue" is a brief tale about a man whose car breaks down and is repaired through the generosity of an alien visitor. Perhaps generosity isn't quite the right word...
John Crowley's "Snow" introduces a new, high-tech method of remembering a loved one after they die. It has its complications, both technical and emotional.
Terry Bisson's "Bears Discover Fire" is one of my very favorite stories. Enough with super-intelligent aliens and artificial intelligences! What would it be like if ordinary animals became just a little bit smarter? Well...
Greg Egan stretches the imagination with "Wang's Carpets," a new kind of life that exists in the same physical world as humans, but several layers of abstraction away from us. Sort of...
In Ted Chiang's "Story of Your Life" a mother pieces together the narratives of her life and of her daughter's life. It's a little hard to follow without some translation.
Please don't let my taste affect your reading more than it should; all thirty-six of these stories are very good. I suggest reading every one of them then trying to select your own top five. It's interesting to experience some small fraction of Gardner Dozois' pain in selecting them.