Hong Kong was a British colony on the south Chinese coast. It was acquired by the British during the nineteenth century Opium wars, so not only did Britain force the Chinese to allow British traders to import Opium into China but we took some of their land as well. Much of Hong Kong was only leased to Britain with the lease expiring in 1997, and Margaret Thatcher handed the whole of Hong Kong back to China at the end of the lease.
After over a hundred years of Hong Kong being run as a British colony with almost no sign of democracy, in a wonderful example of Conservative hypocrisy the Conservatives introduced an element of democracy into the governance of Hong Kong in the run up to handover to China. But they did negotiate an element of autonomy and a continuation of the Capitalist economic system, though mainland China has subsequently segued from hardline Maoism to dictatorial and undemocratic free market Conservative Nationalism, so this may not have been much of a concession by China.
Many people in Hong Kong were not happy with being handed back over to China, because it has a poor human rights record, however there was no referendum because this could have meant war with China. 
Amnesty International is concerned that the right to free assembly has been compromised and excessive force has been used against demonstrators and about other issues stated below.
Participants formally complained of excessive use of force by police who had used pepper spray and punched and kicked protesters.
The public felt able to protest against this which would not have been possible in an extreme dictatorship totalitarian state.
Radio personalities felt they had to resign after calling for greater democracy and large scale self-censorship is feared. Despite this a wide range of opinions are expressed in Hong Kong.
There are concerns that the independence of the judiciary is being eroded.
Freedom of information may be eroded by labelling sensitive material that should be in the public domain state secrets.
Freedom of religion is not respected, members of the Falun Gong religious group were arrested at a peaceful demonstration and convicted of public obstruction, whatever that means. They allege police violence against them. Fortunately an appeal court reversed the convictions but things could ealily have ended worse for the demonstrators and other peaceful demonstrations may have been deterred.
Amnesty International is concerned about failure to protect women victims of domestic violence and other issues.