The setting of the story is Paris in the early 1840's.
Why Paris? I guess it's connected with glorious and most romantic status of this city in contrast with it's dark corners and creepy mysteries. The city produces some Noir effect, although I do not sure, Poe was acquainted with this cultural wave.

        While the dark, smoky room creates a Gothic mood, it also seems decidedly anti-Gothic. People talking, thinking, and smoking pipes in a library seems stable, calm, and not very scary or creepy. (Unless you count Dupin's frighteningly long explanation of how he solved the mystery). There's even something comforting about it. It's a setting perfect for the coldly logical explanation of how Dupin locates and purloins the letter.
Poe just isn't interested here in external details. The story might as well take place in Peoria, Illinois as Paris, France (although Paris does lend a romantic, exotic feel to the story); and if you changed a few of the details, it could just as easily take place in 1945 or 2045. But that doesn't mean setting isn't important.

           Now I have to post some information connected with author, his social and historical background.
Poe lived at the beginning of the 19 century. The Victorian Age in Britain  and prospective development of naive and yound United States. Edgar Allan Poe could be claimed the creator of detective genre of fiction, moreover he's usually mentioned as predecessor of such giants of thrillers as H.Lovecraft and my adorable Stephen King.
Poe's life itself was painted in dark colours. His childhood he spent at cemetery. The school was so poor that children had to study near the crosses and tombs.
The end of his life is  also quite mysterious - found dead on the bench. A good plot for thriller, isn't it?
And I can't but mention the mysterious visitor of his tomb.

            The Poe Toaster is an unofficial nickname given to a mysterious person (or more probably two persons in succession, possibly father and son) who, for over seven decades, paid an annual tribute to American author Edgar Allan Poe by visiting the stone marking his original grave in Baltimore, Maryland in the early hours of January 19, Poe's birthday. The shadowy figure, dressed in black with a wide-brimmed hat and white scarf, would pour himself a glass of cognac and raise a toast to Poe's memory, then vanish into the night, leaving three roses in a distinctive arrangement and the unfinished bottle of cognac. Onlookers gathered annually in hopes of glimpsing the elusive Toaster, who did not seek publicity and was rarely seen or photographed.
According to eyewitness reports and notes accompanying offerings in later years, the original Toaster made the annual visitation from sometime in the 1930s (though no report appeared in print until 1950) until his death in 1998, after which the tradition was passed to "a son". Controversial statements were made in some notes left by the post-1998 Toaster, and in 2006 an unsuccessful attempt was made by several onlookers to detain and identify him. In 2010 there was no visit by the Toaster,nor did he appear in 2011 or 2012, triggering speculation that the 75-year tradition had ended.

Finally I managed with my credits and found time to print smth for my blog

So, I've read the story few weeks ago. As I expected I've read it before, so I had slight deja vu feeling.
Moreover the plot reminded me a novel from Doyle's Holmes Adventures called "A Scandal in Bohemia".
Maybe Doyle was inspired by Poe's piece of fiction...

I wouldn't disclose the plot, because it maybe a spoiler for some future readers.
I'd like only mention that it connected with politics, monarchs, French police and C. Auguste Dupin.
Of course it's not as thrilling as "The Murders in the Rue Morgue" or as mysterious as  The Mystery of Marie Rogêt.