In the spirit of full disclosure, I must point out that I have never been able to finish a John Updike novel. I've tried many times, and each time I came up empty. It's possible that my tastes are simply not compatible with Updike's very thick (as opposed to dense) style, although I doubt it, as I'm a fan of many writers whose writing could be similarly described. I don't know what it is, but I'm not going to choose the occasion of his passing to try and figure it out.
Because really, my opinion of Updike's fiction doesn't matter. He has made his mark on the vast landscape of American literature -- not just that of the 20th century, but the whole of it. Since I've been aware of him, he -- along with Roth, Bellow, and a few others -- were considered the gold standard, and each of them have achieved immortality. They will be read for centuries, and their humbling prolificacy, particularly Updike's (although lately Roth is really cranking them out himself) showed what it really meant to be a writer, and to live as a writer: in short, for that to be what you are.
Updike's output is truly staggering: 27 novels, 13 collections of short fiction, 9 collections of poetry, 10 collections of essays, and 1 play. He won two Pulitzer prizes, for Rabbit is Rich and Rabbit at Rest, and was perversely denied the Nobel Prize, I guess so the committee could squeeze in Dario Fo and Elfriede Jelinek. His last (or most recent, at least; who knows how many unpublished books are on their way) novel is The Widows of Eastwick, a sequel to his famous The Witches of Eastwick. That was published last year. His last (or most recent) collection of stories is slated for this year, and is called My Father's Tears and Other Stories.
As someone who does not count himself among Updike's legion of fans (which is not necessarily the same as "admirers", among whose number I do count myself), I can say without hesitation that Updike was unquestionably a giant of American fiction.