I've got to add, because O'Neil meant a lot to me personally.
I honestly think that there is no writer whose work I've read more of, or more often, than O'Neil's.
The Batman books of the 90s, for which he was the group editor, got me into comics.
His book "The DC Comics Guide To Writing Comics" taught me many important techniques, which I still employ both as a writer, and as a critical reader.
His revamp of Oliver Queen made that character one of my favorite heroes.
There was a humanistic pathos in his writing that spoke to me. Not only as a fan and as a writer, but as a person, I would not be who I am today without O'Neil's work.
And even if his presence in recent years have been largely through interviews, I will still miss this presence.