What are colleges looking for in these essays? Is it simply a statement of why you want to go there, citing things such as an activist student body or state of the art science equipement? What makes your essay stand out from the rest, because I’d assume many people talk about the same things.
Write about how you will benefit from what the college offers. They know that they have a great science program etc. They don’t want you telling them that. They know that e.g. Boston is a great student city. Etc.
A thousand times @TomSrOfBoston’s answer. It’s not about noticing what is great about the school, it’s about noticing how the school is great for you and how you will be great for the school.
Imagine you are King Arthur trying to talk the sword Excalibur into letting you remove it from the stone. “Well, um, you are really good at cutting things” is not going to get you very far. 
Try this as a thought experiment: Imagine what your 4 years at that school might include. Professors you intend to take classes from, clubs you intend to join (or start!), research you would like to do, special talents you bring that the school caters to, etc. Now do the same exercise for other schools you are applying to. Notice the details that only show up for this one school - those are the things to emphasize in your essay. Whatever it is that makes the school a unique fit to you, and vice versa.