Read this great article about him in the New Criterion. I have to confess I've never really got Stevens, and have had a hard time getting into his work. Logan claims that Stevens' rare stretches of magnificent lines "justify the acres of dull philosophizing lacking the odor of a necessary world," but I'm not sure that they do. Such moments come quicker and with more depth in Yeats and Frost, and even when they don't, you can settle for a different sort of greatness by taking the words slowly and allowing your imagine to fill in the landscape behind them. Stevens, not so much.
I think Logan gets Stevens, Whitman, and probably much of modern poetry in general, perfectly with this line:
"The magnificence of Stevens comes at a cost, the same cost we pay for Whitman: logorrhea of an uncharming and embarrassing sort, absurd notions, passages too private with their own pleasure, tone-deafness, lofty ambitions insufficiently grounded, and gouts of gimcrack philosophy."
With Whitman, it's a price I'll gladly pay for the times when that expansiveness happens to capture something great. With Frost and Yeats, I'd say there really is no price at all (maybe with Frost you pay it in enduring the minutiae of a New England winter, but he's such a cantankerous old crank for details you can't help but love him). But for Wallace Stevens, meh... pass.