The original Jaiman was 96 pages long, and the new one is 192. There are also several new books that zoom in on Jaiman, like Xaar which details a specific region in the northwest, and the Green Gryphon Inn in which details a single settlement in Jaiman. An updated Haalkitaine is almost ready too. There is another region book in the works that will detail the northeastern part of Jaiman, and add a lot of new info on the Taranians along with the sub-shuttle system.
The original Eidolon was 158 pages and the new one is 265 pages.
Cloudlords was 50 pages, and the new one is 115.
The original 96 page Emer from the box set has been turned into 4 books, with Emer III being 202 pages in length. An update of Emer I & II are in the works, and Emer IV is on it's way as well. That will will probably be 800 or so pages of material just on Emer the continent.
Sorry I realize I am focusing on page counts here, and that's not really what you asked, but the question probably needs to be "what wasn't updated or expanded on?" I think the maps from the old books didn't all get updates, but that's actually kind of nice because if memory serves me some of them are Pete Fenlon maps.
In my opinion the main selling point of all the new material is how it is all woven together into a cohesive whole. The original books were created by various authors who wrote about a particular location, but there was very little to tie those locations into a bigger picture. The new material seems to be written with a master design in mind, or at least that is the impression I get. You have the encompassing master atlas timeline, each region book has it's own timeline that calls out stuff specific to the region, and events in one book are sometimes tied to and influencing events in other books. A good example of this is the Lankan Empire, the Dragonlords, the Alliance, and the Jerak Ahrenreth are all trying to influence things in Eidolon and vie with each other at the same time. All of those groups are detailed in works outside of Eidolon, but got woven into the book in ways a GM can use to create tension, intrigue, and open the door for players to travel to regions in other books.
Some of the original books aren't regarded as canon by Terry, and at least one of them Curse of Kabis substantially departs from canon. Curse has a well thought out adventure in it, but honestly it's almost like it's not set in ShadowWorld.
I think most folks around here like the original books, I've always liked Demon's of the Burning Night & Nomads of the Nine Nations, but the new books really shine because they are more like parts of a whole rather than a lot of little independent islands of information.
What the new books do not do do is give you so many specifics that there is no place to insert your own creative elements to make the setting something unique to your game table. That's a key element in setting design in my opinion. You give the GM enough information so that they know the setting and are inspired to create games in it, but not so much that it stifles their creativity by answering all the questions and filling in all the blanks.
