Nawaz Sharif is Pakistan's most popular leader today. The long march only confirmed this, yet he has restrained himself from launching an all out attack against the Zardari government. He has become somewhat of a better speaker after his years in exile and seems to be genuinely interested in making this system work. He was a protege of Zia Ul Haq, just as Zulifqar Ali Bhutto was Ayub Khan's. He worked extensively in the 90s to under mine the PPP governments, but his ouster and exile by the army when the was the PM made him realize the futility of doing deals with the generals.
Still I am not sure that Nawaz Sharif is all that changed a person. We thought the same way about Zardari as well and let's be frank if it was Nawaz Sharif in power, it very well may have been Zardari running the long march.The last time he was the prime minister with an overwhelming mandate - he did everything he could to become another dictator. In fact, he was planning to introduce the shariah and become the Amir ul Momenin when he was removed by General Musharraf in October 1999.
Still, he has managed to avoid politics of confrontation if judged from the standard of Pakistani politics. Its a good omen that he has decided to support the PPP government until it completes its term. The two party system has to work in order for democracy to deliver, and for this the leaders of the two parties have to become better versions of their past selves.