I don’t think it is the required number of words that will dictate the quality of your essay. If it is easy to read, written with clarity and evokes some emotion for the reader, it can be short and be very effective.
Depending on the taste of your reading audience, consider what they expect before you start writing. Are they like me – I don’t like too many metaphors, I find they distract me from the enjoyment of reading what should be an interesting read. I don’t care if they are long or short but I like to be able to take something away from what I read. A feeling, something to think about long after the piece has been read and so on.
Then again, when I was taking first year English I got turned right off with reading anything. I think what finally finished me off was no one else, saw what I saw in the works. I hated Who’s Afraid of Virginia Wolf, and the last straw came with my opinion on what the poet was trying to express with The Little Red Wagon or some such other short poem. The prof didn’t agree with my interpretation and although I got a good mark overall, he was not impressed with my opinions.
So is it any wonder I am a business copywriter and would love to be able to write a good essay but find it very difficult? I started with small newspapers and concise was the watchword, it is a habit and I love cutting drafts down to size. :) One of the most pleasant things about being a writer is finding just the right word or phrase to express something.
So who is your audience, if you have a word limit you feel is too short ,that is a challenge for you to find the just the right words, the most evocative language to get the reader to feel something, learn something or just enjoy a good read where they reflect for a few moments after they finish your essay.