I finally got around to read through this setting book - 110 pages of pure setting information takes a while to get through.
The book starts with a small introductory story that continuous along through each chapter. In fact the setting information IS the story as the character in the Preface narrates the history of planet Earth, starting at the Bronze Age and continuing all the way to the New Age (2053).
It is an interesting setting, interweaving mythology and horror with our real world, changing the source of talents during the different ages. As an example, most of the time the gods provide the powers, the occult has its own source of power, modern times develop psionic abilities and the New Age uses cyber implants to harness/enhance powers. Clockwork technology is available during the early modern age, too.
So, what do you get? Everything you want to play, really. During the Dark Ages you could create a Fantasy like feeling, including dwarfs, Elves and such if the campaign is set in northern Europe. The Iron Age sets the stage for nice adventures within the Roman Empire, hunting monsters (aka aliens) - or fighting Germanic Nations. Or use the Egypt background to fight the undead hoards of Anubis during the Bronze Age. Fight the occult during the Dark Ages, be a Crusader and free the Angels of Heaven, subjugate the Baltic area during the Middle Ages, support the settlers in the new world of the Americas during the Early Modern Age or fight occult Pirates, use Clockwork devices to win the battle against evil in London, be part of WWII and stop occult Germans from exploiting secret powers, use your cybernetic enhancements to infiltrate corporations in the New Age.
These are just examples, drawn from inspiration while reading the book. I think I could fit a good part of my adventure collection from different settings, rule books and game systems into the Shadowed Earth. Maybe not as vast as some settings are described, but a city like Freeport I could fit in somewhere and have fun with. Maybe I stretch the canon of Shadowed Earth a bit, but hey: the author encourages this! It is a 'alternate earth' after all, so the GM can do what is necessary.
Call of Cthulhu? A very easy fit for this ... maybe an interesting twist to the Shadowed Earth canon, too. Steampunk Victoriana? Sure, somewhere in London - evil is all around to fight. Alien Hunting? Yep, the world is full of aliens and they are hiding behind myths and sometimes in plain sight. There was a time where aliens could enter Earth very easily. Find them, kill them, save humanity.
Although I read the book cover to cover, I think it is not really necessary as each Age is more or less self contained. You could skip some pages if you find them uninteresting at that time, just read the side bars as they give a quick overview about what happened or is presented on the pages you skip. This helps getting through the book much easier without missing a necessary part.
The only thing that is missing are some good descriptions of possible societies and groups. Something that puts a face to the evil, to the occult, to the hunters and eventually to the players. I think this is where additional books come into place, but I really would have wanted a handful of names, characters and hints how to place the players into the setting.
As it is, Shadowed Earth is a very well done setting that provides a lot of possibilities and gets your imagination going. But to place the players into it, the GM has to do a bit of work creating groups, societies, characters, allies and adversaries.
As stated before, it is easy to take my "Savage Worlds Rome" setting book and get going with the Shadowed Earth. Or my "Crusaders of the Amber Coast" to cleanse the Baltic area from all evil. Or "Call of Cthulhu" to make sure the time is not right for certain beings. Be a hero and fight chaos beings with the "Solomon Kane" setting book. Sail the North Sea with the help of "Mythic Iceland" and bring christianity there. Revive your old "Cyberpunk: 2020" stuff and sneak into corporate buildings.
This is extremely easy to do and I like the idea to be able to do so. Finally a setting that is smart enough to incorporate all my favorite setting books while providing a solid ongoing background story that is always good for a twist.
I'm curious when the author writes some kind of time-travel add-on for the Shadowed Earth so you can walk the Ages of time with one group of characters for a long lasting campaign ;)