If I may make a few notes...
I was an almost original Realms fan, dating to the day the original AD&D Boxed Set came out. (Original Realms Fans were fans from before the boxed set, when Ed was just writing articles in Dragon Magazine).
As we moved into the 90s, I drifted away from the Realms, primarily because they decided to run three "real world" scenarios on top of each other: Horde, Maztica and Marco Volo. I wanted a fantasy world, not a (bad) simulation of real-earth lore, so I abandoned the Realms.
I bought the FRCS when it came out in 2001... and then recoiled at the level of detail it had. It really wasn't a good product for introducing me back to the Realms. In fact, it was awful. A really great resource for established DMs? Probably. Newcomers? No.
The "Grey Box" set was fantastic because it concentrated on the areas of Waterdeep, Cormyr and the Dalelands - the places of Ed's campaigns. It gave an overview of the world, but concentrated the detail. As a result, it was a great introductory set.
The FRCS? Not so much.
I rather hope the 4e FRCS books will be more similar to the Grey Box than the 3e FRCS. Later, I bought the 1e books that expanded the other areas of the Realms, but they were less scary then.
Cheers!