The Prologue Room is only open to the public during summer, but it is free to visit, and is a fairly interesting place for anyone interested in history or aviation.
I liked how comprehensive the Prologue Room’s collection of scale model McDonnell Douglas-related aircraft is; they are interesting to look at, convey history, and show how military and commercial planes have evolved over time. What I didn’t like was how the history of Boeing has been shoehorned into the displays; the Prologue Room does an excellent job of relaying the origins and history of McDonnell Douglas, but you’re not going to learn much about the early days of Boeing beyond what early aircraft it built. Sure, there are models of new Boeing airplanes, but no one has even taken the care to update the wall-mounted product timelines since Boeing and McDonnell Douglas merged (and that was in 1997!).
The highlight is undoubtedly the full-size Gemini space capsule; astronauts actually came to St. Louis to sit in that very model and make suggestions on where to put control switches! For space buffs, this alone is worth the visit, & I enjoyed seeing it.
I also like how it is relatively unknown outside Boeing circles, because that means no crowds to contend with. In fact, at one point for a five minute stretch I was the only person in the entire Prologue Room! Another upside is that visiting the Prologue Room is not a big time investment, even if you go in-depth and read a lot of the informational displays.
The biggest downside is that its operating hours make it an inconvenient place to visit; it’s currently only open to the public between June & August each year, and only open Monday thru Friday during those months! Also, when you’re trying to park, it’s easy to make the mistake of turning into the factory entrance road (which has a manned guard booth), instead of the gated parking lot (which is the only place visitors are allowed to park).
Unless you’re a history or aviation buff, or looking for something free to do during summer, you’re not missing out on too much if you skip this spot.