Writing a review is not the same as writing a summary, you are correct. In a review, you must briefly tell what the work is about but more importantly, how successful the author is in conveying his ideas. You must analyze the work and respond to it, explaining what it means and what it means to you. You will be describing, analyzing and reacting. You can ask yourself what the author’s viewpoint or purpose is, what are the author’s main points, what evidence the author employs to prove his/her theories, is the evidence credible? Also ask yourself if the author gives enough evidence to support the points. Some additional things to consider is how the work relates to other similar works – is it a rehash of the same old ideas, or is it something new? Is the author qualified to write about the subject? What is the writing style like? Is it appropriate to the subject matter?
With regard to Self Reliance, what is the main point? The author’s thesis is that we should “rely” on our own minds (thoughts and ideas) and not on the minds of others. His point is that our ideas are important because they are ours:
A man should learn to detect and watch that gleam of light which flashes across his mind from within, more than the luster of the firmament of bards and sages. Yet he dismisses without notice his thought, because it is his
He goes on to encourage people to trust themselves, trust their views. To envy the thoughts of others is ignorance, to imitate others is suicide – better to take yourself “for better or for worse.” He encourages people to be nonconformists, to be individuals, to be “self reliant.”
Emerson was a skillful writer – many sections from this essay have been taken out and turned into aphorisims, such as: “Whoso would be a man, must be a non-conformist.”
If you go through the rest of the essay and answer the questions above, you will wind up with a good review. Also, read the "critical overview" here on eNotes to get some other ideas about how to write a review.