What is the legacy and impact of the incident at Tiananmen Square in 1989?
I would argue that the legacy of the Tiananmen Square demonstrations of 1989 was that China actually reduced its openness and slowed any movement towards democratization that might have been happening.
The Chinese government is extremely concerned that its people might become angry enough to cause serious social disruption. This fear was intensified by the fall of communism in Europe and by the Tiananmen demonstrations. This led to a pretty serious crackdown on the part of the government that continues to this day. For example, the press has reported widely on the fact that any moves towards any sort of demonstrations (in the wake of the Arab world's rebellions) have been swiftly crushed by the government. In addition, the government continues to heavily censor the internet.
Since Tiananmen, there has been a great deal of opening in China's economy. However, there has been, if anything, a move away from openness and democracy in its political system.