He is a legitimate shutdown defender, but I'd peg him as a solid #2. He doesn't have the offensive upside you'd want from a number 1, but he's absolutely one of the better shutdown guys when it comes down to it. A guy I would trust in any situation against any player. When he went down last year, and wasn't replaced, it showed. Johnny Boychuk did a reputable job filling his shoes, but then it became apparent the strength of this d-core when all three are there, and that losing one of them is a big loss. They are all that important and that good.
what he said...
One of the better #2 guys in the league, but I have to add that - in my opinion - there aren't 30 "Number One" guys in the league.
When I think of a "true No. 1 Defenseman". I think of a guy that you play in every situation: Man-Up, Man-Down, up by one goal with a minute left, down by a goal with a minute left... the guy who carries the team in ALL situations.
Case in point: (looks around to see if there are any Sens fans in the area) - Karlsson... I don't think of him as a prototypical Number One Defenseman... Absolutely one of - if not THE - best offensive D-men in the league. Absolutely. And a guy I would ABSOLUTELY love to have on my team (esp if Krug weren't here). But, despite the Sens fans argument that "He's a good defensive defenseman because he keeps the puck away from the other team" - eventually, there's going to be a 2-on-1 on the guy. So the question is: when that 2-on-1 occurs, does your heart skip a beat or 4? Or are you relaxed and saying "No problem - he's got this".
A true No. 1 should never make your heart stop in a defensive situation.
A true No. 1 should be good or great at ALL aspects, and frankly, there are few of them in the league... Doughty, Weber... you know the names.
So - like Master Boychuk said above... Defensively - DS is one of the better guys in the league. I would trust him going against anyone. In fact during the playoffs a few years back - when he was playing alongside Z, DS was the man... he was (in my opinion) our best defenseman... (at least defensibly - far and away)
But his lack of point production keeps him out of a "True No. 1" slot, in my books. Still a guy who would be welcomed on ANY team in the NHL, and a guy who would be "the best defenseman" on a number of them...but not a No. 1