Steven den Beste puts it best, I think:
In 1974 he was the man this country needed, and was where we needed him most. I respected him, and I liked him, and I voted for him in 1976. I still think this country would have been better off if he’d won instead of Carter.
He wasn’t a great president, he probably wasn’t a great man in any of the usual senses of that term, but that didn’t matter.
He was decent, at a time when decency was vanishingly rare, and that made all the difference.