What is the most important aspect of the Opium Wars?
To me, the most important aspect of the Opium Wars is that they were wars that were conducted so that Britain could force China to allow the British to bring opium into China to sell. The British needed to sell opium to China. When China banned the trade, Britain went to war.
Britain needed tea from China. They had to pay for it with silver and had nothing to sell the Chinese. This meant Britain's silver reserves were leaking away to China. So when the British found they could sell opium to Chinese, it was great for them. Now they had a way to get their silver back from the Chinese.
As I say, China banned the trade and Britain went to war to force them to resume that trade.
So, to me, the most important thing about these wars is that they were fairly immoral from our point of view -- they were fought to force China to allow Britain to sell drugs to the Chinese.
You could also argue that the most important aspect is that the wars ended with unequal treaties that gave the British all sorts of rights to China -- rights that essentially made parts of China subject to British law and not Chinese law.