The museum itself is never too crowded and has a variety of art on display that is both history and unique and thought-provoking, which is the reason I gave a "very good" review.
If you don't get tickets online beforehand, they have kiosks to purchase tickets so you don't have to stand in line. I was surprised by how many people didn't take advantage of the nearly 20 kiosks available. They're very easy to use.
But, and I have no idea why, the floor in that museum is not kind on the feet. I spent two days walking around NYC and my feet were fine, but just after 20 minutes of walking around the gallery on the 4th floor my feet were screaming. I feel so sorry for all of the employees that have to stand on that floor all day.