Entering the Postal Museum from the Union Station side (not sure if there are other entrances), you have to look at one of the table maps to realize you're not in the main museum area, but the second floor of the three-level venue. The second floor housed the main stamp gallery. Using the near entry to the exhibit, I wandered through a broad variety of stamp styles, histories and even an in-person stamp creation display. The exhibit also ventured into the lesser known historical uses for stamps and Alexander Hamilton's contribution to stamps.
Venturing to the main exhibit floor, light and displays fill the main space. What struck me both on the second floor and throughout the first was a complete lack of flow. I've been to nearly all the Smithsonian Museums in DC and several private, but here I had no clear idea where I should start any part of my journey about learning about the postal service. While each exhibit was colorful and informative, oftentimes finishing one ended up in the "finishing" end of the next, so if you worked your way out, you experienced the next exhibit in reverse.
Though I admit not being a huge history buff when it comes to postal systems, I have to say that despite the polish of individual exhibits, the whole was largely underwhelming. I think they would have done much better to build a designed flow, rather than throwing entrants first at stamps, then a randomly curated courtyard and a host of unordered postal exhibits.