Having watched the movie myself and reading some of the comments/reviews with regards to the movie prompted me to post something in fairness to the movie.
I feel that the movie was meant to let audience have a feeling that the leads in the movies are lost. If we were to think of the backdrop of the movie, set in the late 80's, Tiananmen incident, the chant for democracy, all this would have let you understand that the China then was not a China that many could understand.
The China up till the 80s was probably such a controlled and suppressed place to live in, and when these suppressed feelings and emotions were suddenly set free, it was like an explosion. The literature and external factors began influencing the way the people viewed and did things. This could explain the "mindless" love making scenes as the desires to love and to have sex were probably something that was not openly displayed or demonstrated. Freedom is what everyone wants, but the maturity to handle the consequence of the actions brought about by freedom might not be something that everyone can handle.
The movie also explores on people who dare not love. All because they fear losing it. I personally felt the characterization was done quite well, and was aptly shown by the character Yu Hong. Love is not something that can be explained logically or defined in any one way. The insight to the characters views and actions in this movie shows that clearly.
Summer Palace is a movie worth watching, but it might not be a movie that is for everyone. Keep an open mind and try and understand the time and country this movie is set in, you'd probably appreciate the movie much better that way.
