Mitt Romney came into the convention with two goals in mind. Increase likability, and demonstrate competence. The American public needed to accept him as a decent human being and as someone they could see as their President. By these standards the speech was a glowing success. Granted, his policy prescriptions were vague and limited, but this is one of the advantages of being the challenger. When the public believes the incumbent has failed, they are not seeking detailed policy plans (you could argue the public is never seeking detailed policy plans), but rather certainty that the new team is moving toward a new direction that they find acceptable.
Romney and Ryan prosecuted the President’s last four years with devastating affect. The President certainly entered office in a tough economy and faced a Republican Congress that was unwilling to bend in the second half of his term. Voters, however, will clearly remember the first two years in office – the years when Democrats had a filibuster proof majority in the Senate and large majority in the House – as a time when the administration made the choice to fight a bitterly partisan battle on healthcare.
While the speech was by no means a knockout punch, it solidified Romney as a solid candidate who has a fair shot at winning. Given the stagnant economy, and the general discontent with the direction of the country, it could be good enough.