If the creators care enough about the small details, imagine what they do with the big ones. That kind of meticulous detail can only bode well for a film. Every SINGLE piece of clothing which the characters wore, down to cuff-links, handbags, hair pins and shoes were of the era.
First, the sets and costuming were near perfection. As such, and knowing that I have a tendency to sometimes exceed the number of allowed characters, I'd like to add just a couple of small things.
Other reviewers at the top, when sorted by Helpfulness, have already covered much of what makes this film so exceptionally good.