Since Willa Cather's style in My Antonia is different and the story doesn't quite follow a normal plot, what makes the writing stand out?

Willa Cather is recognized for her brilliant sense of place in her stories.  She recreates for the reader a sense of time and circumstances unique to the region in which she sets her story.  The sweeping plains of Nebraska, the hard cold winters, the lush spring, the fertile summer fields with the hot sun are all very real for the people of the area.  For the reader it is a timeless experience to somewhere they do not know or have not experienced.  She captures an image, like a photograph, of people and situations that no longer exists.  But when they did, they were the foundation for the rich farmlands of the midwest. 

I believe it is in the first book that Jim and Antonia experience the sunset with the plow sitting against its backdrop of a red, evening sky.  My book is not at my elbow.  In another passage in the same section, the visit Jim makes to the Shimerdas to find them sleeping in small burrows they dug in the ground of their cave is a startling image for the modern mind to imagine.  The characterization of Jim's grandfather, who reads the Bible every night at supper or of the Russian serfs who recount the story of the birdal party attacked by wolves in Russia.

The book is a strong collection of imagery and characterization more than anything.  The great midwest, the immigrants who settle it and the Americans who recognize their place in the scheme are much of the reason the book stands the test of time.