Leadership
Jack leads by example. He's up front and in there with his people, not behind a desk. He shares equally, if not more so, in their risks - he does *not* lead from behind, but from point.
You can trust him to do everything he can for you, but also know he'll go for the mission if that's what has to be done. He won't sacrifice you for the easy way out, but if you have to 'go down' you know he's tried every other way he can think of.
He will admit to his mistakes [not all the time, but a lot more than some CO's I worked with in some pretty hairy situations]. He listens to his people [at least at base... sometimes it's harder to do in the field at a snap]. He sees his command as 'his people', not just 'mission assets'.
He does not 'dump' on those below him when things go to hell, even if they weren't his fault. he takes the heat and then passes it on as any good troop commander should. and whe it goes well, even it if was solely because of him, he makes sure the kudos go to his people, not him.
As a CO, I would follow Colonel Jack O'Neill just about anywhere.