I did like Gilead. Most of Robinson's books (and I've read them all) didn't appeal to me enough to want to re-read except Gilead, and it may have been because of the epistolary style.
Also there are: The Color Purple The Screwtape Letters (hilariously ironic) Flowers for Algernon Anne of Windy Poplars A Woman of Independent Means
Also there are:
The Color Purple
The Screwtape Letters (hilariously ironic)
Flowers for Algernon
Anne of Windy Poplars
A Woman of Independent Means