An extremely skilled polemicist. But that's more or less all he is. He's not as clever, profound or intellectually interesting as he likes to think. Far too frequently (and on a bewildering range of subjects) he has taken the position of the bigot and the bully; anyone who has the temerity to hold a view opposed to Hitchens or (heaven forbid!) to actively disagree with him is at best an idiot and is usually attacked as being utterly malign. Of course that's a fairly common trait of those who passed through youthful Trotskyism of one kind or another, but that doesn't actually excuse that sort of behavior.
That said, he's vastly superior to his brother who has all of his faults (though they manifest themselves differently, of course) and a few more on top. And is basically an out-and-out fascist.
I will add that since his death it has become clear that he is mostly remembered as A Character rather than for anything that he actually wrote. I suspect that he will slowly fade from public consciousness, ala Arthur Koestler.