I was young at the time (35), but like almost every Pakistani I was overjoyed when Zia toppled Bhutto (and hanged him later). I have written elsewhere about how much Bhutto damaged Pakistan (https://tribune.com.pk/article/33546/we-will-never-forget-nor-ever-forgive-you-mr-bhutto). Indeed, I still believe that he was responsible for the break-up of the country, by damaging what remained of Pakistan by nationalizing industries and dividing the country by using the Sindh card.

But in hindsight, I believe that he should not have been executed. I still think he ordered many people to be killed, but then, as pointed out by many people at the time, even American presidents had done so. As I grew older, I gradually came to oppose the death penalty, which is why hanging Bhutto was the biggest mistake Zia made. If Bhutto had been freed, he would have won the next elections and hanged Zia (as he'd threatened to do). But of course, Zia could have saved himself by leaving the country, even though it's doubtful if Bhutto would have carried out his threat. 

By killing Bhutto, Zia made the PPP more popular, which lead to Benazir and Zardari getting elected, and the country suffering because of their corruption.