Undergraduate / MIT: Playing the piano has always been a pleasure, a strength and a passion for me [6]

I also think it is very strong! The last sentence really brings it all together I think

Undergraduate / 'Chinese common sense and education' - Columbia Supplement, meaningful about books [5]

I also like the second version better, though I think the last sentence should be made a little clearer, as I think some of what you meant to say is lost with some awkward wording

Undergraduate / Common App short anser "Founding a club" [5]

the first three sentences or so could probably be condensed into one stronger, more meaningful sentence. That would help you shorten it and also make your opening stronger and

Undergraduate / 'Beijing is an amazing city' - Common App - Personal Experience and Its Impact [4]

I feel you may want to talk a little bit more about its impact on you. The first two paragraphs focus a lot on the physical things you saw there rather than the specific lessons that you took away from them. Also, the last sentence should probably be re-worded; it sounds a little awkward.

Undergraduate / '58 men who look just like Waldo' - UChicago Essay #2 [7]

I really like the concept and it seems like you executed it quite well. I don't think this essay will prevent you in any way from being accepted

Undergraduate / 'MRI training at Holmes Regional Hospital' - extracurricular activities [2]

perhaps for the last sentence you should explain more why you fell in love with the machines and the people there rather than the safety measures of the machine

Undergraduate / 'My mom sacrifices for me' A person who has had a significant influence on you essay [4]

the last few sentences are the most important when you talk about the effect she has had on you, i'd recommend adding more to that part to further strengthen your essay

Undergraduate / 'Yearbook staff and dancing' - COMMON APP [6]

the transition from the third to fourth period could be confusing, I would recommend perhaps making a better transition from the idea of dance to the yearbook staff