Because he's got charisma. Listening to him talk, I feel like I can trust him
I really agree with that, but I'm desperately looking for something more to back that up for me.
While I don't fall into the "oooh, Obama!" camp ... I do recognize that as an effect, and possibly as an effect that can rally a people, and maybe even unify a government around him and his positions. And that's what it's going to take to break the inertia of the present.
In contrast, McCain's "maverick" tendencies could well lead us into deadlock and inaction.