The sixth-floor museum is a must-stop on any Dallas itinerary. I've been there a number of times, and it is my favorite place to take visitors.
The exhibit contains information about JFK's life and radio and newsreels of the trip to Fort Worth and Dallas that ended in the assassination. It allows you to stand in the same window where Lee Harvey Oswald allegedly stood to get the sniper's view of the road and the grassy knoll. Someone has painted an X on the road to mark the spot where JFK was killed.
On the upper floor of the museum they have space for rotating exhibits.