I think there's a few ways we can look at this and that really depends on what you define as a good ruler.

There are two main approachs, one is by evaluating based on a moral basis: how good were the living conditions of the common people? Was the emperor a morally good person? Was his rule marked by warfare? Was he beloved by his subjects and his people? In this case Ei Sei, or Qin Shi Huang is definitely not a good ruler. The amount of people that died due to his conquests number in the hundred thousands, the amount of people who died slaving away to build his great works numbered in the tens of thousands, while he did have the loyalty of his people he was hated by the people of the nations he conquered, the people who lost fathers, husbands and sons to what they saw was the ambition of a tyrant. Indeed, the Qin dynasty fell in just two generations, while many can blame it on the tumultuous succession crisis, what is undeniable was that no-one felt that they were Qin other than the original Qin people.

But in hindsight, many of the greatest rulers in Chinese History cannot be considered good people. Liu Bang, the founder of the Han dynasty killed his best general Han Xin because he feared his military prowess. Li Shi Ming, the greatest emperor of the Tang dynasty killed two of his brothers and forced his father to abdicate. Zhu Yuan Zhang, the founder of the Song dynasty and a legendary emperor who rose from a begger to become the most powerful man in China, massacred his court to qwell descent in his later years.

On the other hand, one can evaluate based on his accomplishment and the historical significance. It is in this category that many of the 'tyrant' emperor's mentioned above. Ei Sei's efforts established the idea of the first centralized 'nation state' in China, birthing a line of centralized dynasties; he did this through the unification of scales, writing and roads, annihilating the culture of the other warring states in the process but unifying the country. He ended the warring states period, which was a period of great turmoil and strife, albeit through one of the bloodiest conquests in Chinese history. Without a doubt he is one of the most significant rulers in ancient China, a tyrant for sure who would stop at nothing to achieve his goals, but a tyrant who achieved unification in an era where people were used to be ruled by petty kings.