Hell, other than Todd Howard I struggle to think of any that have done it as well.
People want to say Kojima, but everything before MGS didn't exactly set the world on fire and everything post MGS3 has been incredibly divisive.
Spear of Destiny
Pretty impressive, and each of those (with the exception of Spear of Destiny and Doom 2) was a major technological breakthrough.
So I vote for John Carmack.
Not discrediting Carmack's absolute monster contribution to gaming in general, but I'm pretty sure he was more of a tech director/programmer lead than actual game director.