He does not have the kind of experience necessary to run the country. Run anything in fact. He used to be a famous sportsman.
When it came to politics, he started off as a decent chap, but he realised that if he wanted to win in Pakistan, he's going to have to accept, at least publicly, all the stuff that's wrong in Pakistan. Radicalisation, blasphemy, Islamic rhetoric, bigotry etc. So he is now considered a hardliner.
There's also the issue about his close ties with the Pak Army, ISI, radicalized Islamic groups etc.
He may have personal issues too. Too many allegations of drug abuse, which could be true due to his celebrity status.
When it comes to serious political issues, his head's in the clouds. He has unrealistic expectations about foreign policy and security. He believes in having closer economic tries with India due to the demographic nightmare that Pakistan is facing. His number 1 priority is trade with India. But the core issue is Kashmir, without which we cannot move on, so let's see what he does there. He is not pro-US either. Overall, his expectations are a bit unrealistic.