I've read three of his novels: The Hunted, Killshot, and Bandits, in that order. Bandits was a book on tape, and I wonder if that has anything to do with the fact that I liked it a bit less than the other two. But I thought they were all outstanding. It was a good twenty-five years ago that I read The Hunted, yet I remember it in considerable detail, far more than is usual with me--frequently I forget everything but the broad outline of a plot within a few years. I think the reason is the sheer intensity of the storytelling. I don't know of any writer who can create the narrative tension that he does. Well, no, there is one, or at least one book: Cormac McCarthy's No Country for Old Men. And the compliment I paid that book was that it's as good as Elmore Leonard.
But I'm not sure I'll ever read anything else by him. The morally vacant world he portrays is so bleak and disturbing that it's not a place I want to visit very often, perhaps never again. I wouldn't say that Leonard's own point of view is amoral; quite the contrary, in fact. But his portrayal of the other is maybe too vivid.
Any writer who wants to learn how to construct a gripping story, and dialog for inarticulate characters, could learn a whole lot from him. And if you want to read a thriller, I can vouch for any of the three above-named. On the basis of those, I'd call him a genius of the style.