There have surely been many consequences of imperialism in China. I will argue that the following are the two most consequential of these.
First, I would argue that imperialism helped cause communism to take over in China. The British actions, in the Opium Wars, for example, fatally wounded the Chinese state. This led to a situation where China devolved into conflict between various warlords. This allowed the communists to, eventually, become the dominant power after WWII.
Second, I would argue that imperialism helped make China very confrontational towards the West. China feels that it has been seriously mistreated by Western powers and that it, therefore, wants to stand up to those powers at every opportunity. It feels the need to in some way get revenge for the humiliations it suffered at the hands of Western imperial powers. This has complicated relations between China and the West today.