It's probably a personal aesthetic, but the variable stroke widths make it look cartoony. It's also got a tendency to big loops — the a, p, h, and g in the sample all have very large, arched, oval shapes (this is probably what they're referring to as the large x-height). That makes it look exaggerated to my eye, and doesn't help the cartoony appearance either.

But if it is a personal dislike and other people are fans, I can't object. It wouldn't be the first time I disliked an Apple initiative that turned out to be very successful.