Let's name the signs of an essay that make it clear that it is not, for example, an essay, an article, or a grademiners review.
A small volume. The author writes succinctly, the reader quickly runs through the written eyes.
Free structure (composition). In its pure form, works of this genre do not have a strict structure. Allowed to begin immediately with an argument, then move on to the statement of the problem. Or to draw a conclusion in the beginning, and talk about the reasons to leave "for the sweet.
At school, for the convenience of examiners and the writers themselves, it is suggested to adhere to a certain structure of the essay. It is as follows: statement of the problem - arguments (1st, 2nd, 3rd) - conclusion.
Presence of the problem. Despite the fact that the plan of writing an essay has a free composition, the writer's thought should unfold around one problem stated at the beginning of the text. All the arguments voiced in the main part are obliged to illustrate it and smoothly lead the reader to the solution. The conclusion should be explicitly or implicitly voiced.
Individual style. No matter what kind of essay you write: historical or philosophical - an obligatory feature of it should be a bright and rich language, an original style. Such a tradition has its roots in journalism.
The author of a newspaper article risks being forgotten immediately after reading it, so the journalist tries to make his speech memorable. Each experienced newspaperman has a signature technique, a "zest".
When writing an essay, it is important to "include" personal charm and make your text lively, not like others.
Imagery and aphorism. An essay incorporates the best features of artistic and journalistic styles. Both are characterized by imagery and metaphor. On the verge of these two styles most often aphorisms, new non-standard expressions (neologisms), curious language game are born.
To use all this is not only possible but necessary! True, such a luxury is not so easy to afford if you write an essay in English. But in foreign languages too, there are plenty of figurative expressions that embellish the speech.
Closeness to colloquial speech. Do not "dry up" the text. Scientific turns, multi-part sentences, clericalisms, stamps are contraindicated to such a genre as an essay.
The simpler the language of narration, the shorter sentences, the easier the content is perceived. True, this does not mean that the bar should be lowered to the level of slang, jargon, and profanity.
You can find additional information in this Scamfighter review.