When we toured the Vatican Museum the Sistine Chapel is the last room. We went through so many spectacular rooms with great treasures, that the chapel was just another room. It was overwhelming. I suggest people space out the museum and gallary visits and get outside and walk the city.
I've heard that the tourist route into the Sistine is through a long darkened hallway, which increases the impact. Of course, it's widely regarded as the greatest work of art by a single artist. :')