We just got back from a week in the Kansas City, MO area (actually in Fort Leavenworth) and made it to Q39 and Jack Stack.
The first thing the hawker / sales person (waiter) did at Q39 was answer each of our questions about individual dishes with how each was so good it would transform our lives forever (it didn't). It was good, but not life transforming nor the best I've had, and was so loud that we couldn't hold a conversation. Good food should sell itself and not need a hawker.
Jack Stack was a fantastic improvement in both taste and environment. I really liked their food. As said earlier in the thread, it is more expensive (lunch was $125 plus tip for 4 adults and two kids), but well worth it.
If you're ever in the Leavenworth area, there was also a small place nearby called the Tin Kitchen in Weston (small tourist town) that was very good also (rated in the top 20 BBQ places in and around KC). Almost as good as Jack Stack, but much cheaper.