I would be honest. If you are asked why you like Hamlet, the whole play or the character, tell why. And if you don't like the play or the character, tell why that is. No one here or anywhere else can tell you why you like or don't like something.
Did you read the play? Did you understand it? Many students say they don't like a work either because they didn't really read it, it was too hard, or they just didn't like it. If any of this is true for you, say so. If you didn't read the play because you couldn't really understand it, say so and tell why you had difficulty.
Or, if you read the play and understood it and liked it, put some ideas together and tell why.
Reading your question, I'm not sure if you mean the play or the character. You don't italicise "Hamlet," and previous editors have already helped you out concerning the play itself, so I'll answer assuming you mean the character of Hamlet, just in case.
If you are assigned to write about why you like the character Hamlet, you again need to streamline/narrow down your thoughts. Numerous elements of Hamlet's personality have been considered likable by some teachers and critics. I'll suggest a couple you could study.
He is witty. Look at his conversations with others. A single conversation would likely contain sufficient detail for a one-page essay. See his conversation with Ros. and Guil. in III:2, or his conversation with Polonius in II:2. The gravedigger scene in V:1 also displays Hamlet's wit.
Hamlet also possesses an imaginative, creative mind. Study any of his soliloquys, his conversation with the king about the body of Polonius (IV:3), or, again, the gravedigger scene.
Any of the above will provide plenty of evidence for a textual study in which you use details and spot quotes from the text.
A short essay must be very specific, so you will need to focus on only one idea. Did you read the play and see it staged? Have you seen any of the film adaptations?
Shakespeare's plays are meant to be seen and not read; they are meant to be heard. Their power comes in the eloquence of the language combined with the movement of the action. Aristotle said "Plot" and "Character" are the two driving forces of tragedy. You might pick one of these to focus on.
Here are some other ideas:
Pick an act or scene you liked best: I like the Ghost's monologue in Act I.
Pick an element of stagecraft that appeals to you: I liked Branagh's use of mirrors in his 1996 film adaptation.
Pick a character that you identify with: most people empathize with Ophelia, and how she is a supplient destined to suffer.
Pick a favorite passage, a monologue or soliloquy: the obvious one is the "To be or not to be." "This sullied flesh" is also a favorite.
I agree with the first editor. We are not allowed to write an essay for you, but I can help you out with some ideas. One character in the story who suffers greatly is Ophelia. She loves Hamlet. He is cruel to her. Ophelia is dedicated to Hamlet. She is humiliated and mocked by her brother over her love. Her father dominates her as well as her brother. She is a helpless victim of a society that is controlled by the men in her life. She finally kills herself after Hamlet's rejection of her and her father's death.
I believe a character study would make a good essay with the material to back it. However, whatever topic you should choose, you need to be prepared to support it with quotes from the text of the play.