The guy got some things wrong, but he got a lot right (in both senses of the word).
Buckley leaves an enormous legacy, but to the detriment everyone, the right left Buckley years ago. Where Buckley stood athwart the tide of history and beat it back with wit, sophistication, and argument, we today get best-selling Regnery screeds from lowest-common-denominator clowns like Ann Coulter, Dinesh D'Souza, and Glenn Beck. Where Buckley mistrusted government and aimed to slow the world down, he's been usurped on the right by the likes of William Kristol and David Brooks, men who want to use government to remake the world in their own image. Where Buckley flourished in cosmopolitan Manhattan and took delight in life's finer things, modern conservatism has grown disdainful of the marketplace of culture, commerce, and ideas abundant in urban areas (witness the last election, where many on the right weirdly smeared John Kerry as a "latte-sipper"—real Americans apparently drink Maxwell House). In fact, today's Bush/neocon-right is often contemptuous of commerce itself, sometimes calling the voluntary, unchecked exchange of goods, labor, and services—a pure free market—"ugly" and "crude."
The 15-year GOP ascent to power from 1980 to 1994 gave rise to rightist thinkers more inclined toward activist government, just one that was active promoting conservatism. With Republicans at the helm of the federal government, limiting government's scope and reach no longer seemed like such a good idea. So old right thinkers like Buckley lost influence in favor of big government neocons like Kristol, who gave quarter to grand dreams like an imperial presidency, using the federal government to promote conservative values through intervention in areas like health care and the public schools, remapping the Middle East, and other ideas that require too great a belief in the competence and benevolence of bureaucrats and politicians for sensible rightists like Buckley.
I didn't agree with Buckley on everything, of course. But he represents a time when conservatives and libertarians shared quite a bit of common ground—indeed when both philosophies largely sprang from the same well of ideas and influences. I don't think that's the case anymore.
Rest in peace.