So, like many seniors my age, I’ve wrote draft and draft and draft (a whooping total of 9 different essays) trying to create an essay that will really sell the admission officers that will read it. I think I’ve created the best essay I can, but how can I know? What makes an essay great?
Second question: How much of an impact does an essay make on the college admissions accept/deny?
As a senior (I have a college counselor outside of school – siblings are in college at Case Western and Brown), they told me that the personal statements are the defining element in your application as that’s the representation of you outside a few numbers. Personally, I’d ask some people to read it (teachers preferably) and rate it. 
A great essay is something that tells admissions officers something about you that can’t be found elsewhere in the application and that makes you a more desirable candidate.
The importance of essays varies from school to school.
If you’ve “created the best essay (you) can” then I think you’re done.
Read this for ideas:
http://www.■■■■■■■■■■■■■■■■■■■■■■■/uploads/1/0/9/5/109505679/hack_the_college_essay_2017.pdf
A good essay allows an AO to see who you are. The rest of the application show what you do (and how well. ) The extent to which the essay (and recs, which can do the same) matters depends on the school.
As a very very general rule of thumb, schools that have lots of qualified applicants may be more likely to use this to figure out which ones to take.
Something about you, yes. Who you are, yes. But relevant to this college admit review. Not just any writing, but something that reflects what they want, the attributes, Now or during high school, not what happened when you were a wee one. And, “Show, not just tell.” If you did evolve, let them see it, not just have to take you at your word.
A good essay gets them nodding, smiling, that you get it. Many times, parents will say, well, my kid wrote X and got into a reach. But this is more than about topic, alone. The devil is in the details.
A good essay makes me laugh (or at least smile) and think.