To say it's the best kiss that he's had outside of a dream in years would not be an overstatement. The very few moments of physical intimacy that he has experienced since the worlds ended were more impersonal—sometimes desperate, but motivated by a need to make any connection in a universe that's going hell, not by passion or interest. (Maybe the Eight on New Caprica had been different...) Martha kisses like someone who's fully present and making a deliberate decision, not just going for the closest warm and willing body.
By the time he pulls back—breathing is an unfortunate necessity—her face is cradled between his hands and his brain is buzzing too much to form words.