I used to be under the impression that Qin Shi Huang's uniting of the Chinese kingdoms was a huge milestone in Chinese history and a great achievement. However in his book 'China: A History' John Keay downplays the first emperor's conquests, stating that his father laid most of the groundwork and that the idea of a single dominant dynasty wasn't unprecedented (like the supposed Zhou dynasty). Does this ring true?
Sima Qian's Records of the Great Historian contends that while Qin Shi Huang came to power as King of Qin in a good position to the other Warring States, it is what happened after he defeated all the other kings that made him a true Emperor. He abolished the old system of vassal kingdoms (wangguo) in favor of a single unified system that was the basis for Chinese imperial administration for years to come, as an empire (diguo). While the Zhou and Qin dynasties had control over similar amounts of territory, it was Qin Shi Huang's centralization reforms that changed China. Compare the post-Golden Bull Holy Roman Empire, for example, where there were vassal dukes and vassal kings (like the King of Bohemia and King in Prussia), which was not centralized and did not usually have a unified administration and foreign policy.
I would say it was a huge milestone. It wasn't all due to Qin Shi Huang, so that part's true. Qin Shi Huang's father, King Zhuangxiang, only ruled for a few years, so unless your source is alluding to rumors that Qin Shi Huang's real father was the powerful Qin minister Lü Buwei, I wouldn't say the Qin unification was due to Qin Shi Huang's father. I would go a bit further, to around 300 BCE. Qin Shi Huang's great-grandfather, King Zhaoxiang, deserves a lot of the credit too. It was under King Zhaoxiang that Qin won the battle of Changping, generally credited with destroying the power of the rival state of Zhao. King Zhaoxiang's father, King Hui, ruled when Qin conquered the states of Ba and Shu, thus giving the Qin state an advantage over the southern state of Chu. Zhao and Chu were two of Qin's greatest rivals during this time. Qin's unification of China in 221 BCE was by no means a given, but Qin Shi Huang had an excellent base from which to work. Qin was already the strongest power in China by the time he came to the throne.
Qin Shi Huang substituted the fengjian system of fiefs from the Zhou Dynasty (which was absolutely real) and created the zhouxian system of direct control over all parts of the country. In addition, Qin unleashed a great standardization campaign across all of China and expanded China into the south, so that Qin had a more territory than the Shang or Zhou Dynasties.
EDIT: I should note, 221 BCE was when Qin conquered the last of its six rivals, Qi, having conquered the other six between 230 and 222 BCE. By 221 BCE, Qin's unification was basically a given, since only one other state is left. What I meant was that Qin's conquest of the other six Warring States by 221 BCE was not a given. But Qin was already the dominant contender before that time.
These two answers are pretty spot on. One thing I would add is it is more proper to call him "Qin Shi Huangdi". In Chinese, "Huang" refers to a King, while "Huangdi" refers to an emperor. Thus his name essentially translates to "First (Divine) Emperor of Qin". To me, this seems like a common misconception about his reign name.
Also to jump on what xin-cheng said, I have never read anything that said the Zhou Dynasty did not exist. Are you sure you weren't thinking of the Xia Dynasty?