以下是我个人建议，仅供参考~
首先我觉得这篇文章写得略过简单，没有特别出彩的地方，有点像四级考试作文~
然后有些地方我觉得语法不对，写得有点中国式英语
第一句：I am writing to you to recommend a movie for you which shows an Chinese assassin in Qin Dynasty.
The name of the movie is hero,you may be confuse about why an assassin is a hero.
but they do not use it unlimited 这里unlimited应改为unlimitedly~副词修饰动词。
because they know,with great power comes great responsibility.
可以改为：the more power they use, the more resposibility they shuold pay.
The chief actor of this movie is acted by Li Jet ，这句actor应改为role.
In this movie,you would know a truth that a greet knight,for the country and for the people,it is the essence of the Chinese Xia culture.这句中it is the essence中is应去掉，不然一个句子有2个主语了。
he has kung fu ，这个我感觉不应该用has,但我也不知道用什么好
暂时就这些了，希望对你有帮助~