At a population level, it's great. For individuals, it can fail in all kinds of ways. For me: it is not very good because my body has very strange proportions. I'm 6'2", but my waist is barely higher than my 5'1" wife, and my torso is nearly the same length as my 6'7" brother.

In other words, for my height, I have a very long torso and very short legs. I think it should be relatively obvious that an inch of leg weighs significantly less than an inch of torso, so at a given level of body fat percentage, I'm going to weigh quite a bit more than someone my same height with more typical proportions, and thus my BMI reads me as more overweight than it otherwise would.

My point is not that BMI is bad or useless or anything else. My point is that it was designed as a population statistic and that it can be fraught when one tries to apply it to any individual with no nuance. A high BMI should cause one to consider and examine your health and weight. But it should not over-ride specific details about your physiology that point in the other direction.