I've also been there, and in the 6th fl museum. what struck me is why Oswald didn't shoot JFK when his car was coming down Houston street.
JFK's car was coming straight at Oswald's position. Oswald was at a perfect angle, right above him. The car was traveling very slowly due to the crowds lining the road. It was open-top, so Oswald had a full body shot. Yet Oswald waited until the car turned onto Elm and started to speed away, to take a much more difficult head shot.
I have wondered that also. Seems like an easier shot.