I read about 30 this past year as a volunteer. I'd say about 30% were ready to submit/fine, 45% needed a good amount of work, and 30% needed some very serious work. I read maybe one that I would consider exceptional. Perhaps ironically, most of the people who were most confident sending their drafts ("I think it's almost done" for example) needed the most work. Those who were incredibly off base (making excuses, sounding entitled, not answering the question, very poorly written grammatically etc) likely had no idea they were falling into that category.
A fine personal statement made me understand something about you and why you want to be a doctor. It told me what you've done to explore this career, what that taught or meant to you, and was written in proper english with proper sentence structure and word choice. It was also organized in a logical manner with a clear beginning, middle, and end, and a good reason for them to be in this order.
A strong personal statement does all of the things a fine one does but it also does something that makes me want to learn more. For example, it is written in a compelling way, makes smart observations about the author and the field of medicine, is introspective and thoughtful. I really don't care where someone did something, I care what they learned. A fine one tells me they did it and it made them want to be a doctor. A strong one tells me WHY it made them want to be a doctor. What did it make them realize about themselves? About their strengths and weaknesses, passions, interests, etc. What did it teach them about the field they want to go into and how did it do that? Bonus points for proper use of semicolons and gerunds.