We bought the earliest ticket available and once the museum opened, we got in quite quickly. I think the reviews who had struggles with the entry probably had a later entry time or did not pre-purchase tickets and I can see how that would get messy. We decided to start on the 4th floor with the dinosaurs and work our way down. The exhibits were great and our son (who wants to be a paleontologist) was in heaven. My only complaint was the temperature of the building. It was oppressively hot in most of the areas and it really distracted us. We ended up not staying as long and seeing everything because we were so uncomfortable.