After reading the debate transcript, Noah Millman homes in on the "most striking contrast between the two men: the way they understood language – whether they treated speech as a signifier of action or as an act in itself":
The contrast was especially true in foreign policy, where Ryan raised almost no substantive objectives to the President’s policy but repeatedly asserted that the President “appeared” weak because he “called Assad a reformer” or “announced a deadline for withdrawal” or “didn’t stand up for American values,” but it wasn’t limited to that area. In domestic policy as well, Ryan repeatedly resorted to formulations suggesting that announcing a goal – 4% economic growth, for example – was the same as articulating a policy. By contrast, Biden repeatedly resorted to a formulation along the lines of “we said we’d do,” some policy action or other, “and we did it.”
I find the contrast interesting, because it inverts the standard trope of right-wing criticism of the Obama Administration, that all Obama does is “give speeches” rather than leading (I believe Ryan said that a couple of times last night as well).