Your classmates and instructor as an academic audience. You can therefore assume that this audience has read (at least shallowly) the essay you are responding to, and therefore, that they need only a brief summary. This audience is going to be more interested in your response to the text in question. They will expect you to thoroughly explain the points you are making and to demonstrate (using evidence from the text) how you have come to your understanding of this text. In addition, it is likely that your audience will expect you to use a reasonable tone, to respect your readers and sources, and to avoid slang.