Forbidden Kingdoms: Modern is a slimmer version of the full FK book. This one uses the D20 Modern rules to cover the heavy lifting and leaves the rest of the book to focus on what is just Forbidden Kingdoms.
The Pulp Era is not one I spend a lot of time playing in, but it certainly tailor made for adventures. You have many of the advantages of a modern society and still have large areas of land that mysterious, unknown and ready for imagination.
Forbidden Kingdoms (any version) is actually one of my more favorite Pulp era games. It is also the game that helped me see the value of D20 Modern.
The background information covers the end of the Victorian age till WWII and has a great overview of history. Not perfect of course, but perfect for a game.
If you like the Pulp era or any of the books that came out then, then this is a great game to have. I am using it for the history sections and the adventure hooks alone.
[4 of 5 Stars!]