I've always found his calmness, conscientiousness and intelligence attractive. You know he wouldn't miss the crucial detail and he's someone who listens. I find his voice a bit surprisingly 'light' somehow. (Same is true of Colin Firth, that's a fantastic link!).
Lookswise, dunno, have mostly heard him on he radio I suppose. I'm relieved he fits 'socially acceptable image of leader' as that gives him easier access to that game and helps allow for a functioning opposition. Looks shouldn't matter but... they do.