Short answer: Nothing really stands out as "special" about the FR, but it is detailed, generally well done, and relatively straight-forward D&D, with a nice Greenwoodian quality. In other words, it is "vanilla" D&D fantasy, but with a couple spices added in for flavor.
But it is more than that...I think what is special about the FR is that it includes just about everything within the D&D canon. There is a kind of jumbled messiness to it, like a building that has been added on to over many years. If you look at the map it doesn't even really make sense; mountains arise in short little ranges all over the place, with few major uniting chains (think the Rockies, Himalayas, Andes; everything is the Alps or, at best, the Appalachians). Pre-4ed is so ridiculously analogical to the real world, with versions of Egypt, Sumer, Persia, etc...
Despite the jumbled nature of the Realms there is enough to make it cohesive, from the distinctly Greenwoodian names like Impiltur, Anauroch, The Simbul, Waterdhavian (what's up with that?), and of course Faerun (fay-roon)...they somehow manage to be slightly silly and overall pleasing at the same time.
To put it another way, FR is not a slick chain bookstore like Borders or B&N, it is the huge jumbled independent used bookstore like Powells or the Strand that you can get lost in for hours.
Another nice thing about the Realms is that the 3ed hardcover may very well be the Nicest Campaign Book every printed...by anyone. Can anyone think of anything that is nicer? The Golarian book is nice, but doesn't quite have the diversity of the FR book.