First let me apologize for the Wall o' Text. I got a little carried away...
I've been an ED fan for a couple years now. It's a quite good game/system. There's bit of a learning curve for new players. The step system that they use for the dice rolls can be confusing. It can also be annoying to have to look up what dice you need to roll on a chart. But once you get past that it's actually a really neat mechanic in my opinion.
As for what's new with 3rd Edition. They streamlined a lot of the rules, fixed various problems that had cropped up in the system, etc. That sort of thing. They also changed the way the classes work in the game. They give the player more choice in what talents to take and basically what direction to take their discipline in. Every circle(level) the character gets 1 discipline talent that's fixed based on your class, and 1 non-discipline talent that can be picked from a list. So the core disciplines remain the same, but there's more variety in the classes. For example you might have a Swordmaster who focuses on the more social aspects of their class and thus takes the more social talents. While you have another Swordmaster who will focus on the more martial aspects taking the more martial talents. They're both Swordmasters, they just have a different focus.
The world is identical to the world in the previous editions. They moved the timeline forward a little bit to bring it up to the end of the original first edition novels and adventures. The basic story for the game is that it takes place on Earth 30,000ish years ago during the last time of High Magic. It's the same world as Shadowrun. So the levels of magic in the world follow a cycle of highs and lows. While the level of magic in Shadowrun is just starting to rise again, the level of magic in Earthdawn is just past the peak. The problem is when the levels of magic in the world get so high, it allows alien entities called Horrors to enter the world. Horrors are immensely powerful beings that feed off of pain, suffering, and fear. The only way the people of Earthdawn were able to survive this time, called the Scourge, was to wall themselves of with Earth and Magic in massive city size bunkers called Kaers. They lived in these Kaers for several hundred years while everyone that was stuck outside was tortured and killed, or worse. Eventually the magic levels went down, the Kaers opened and the people went out to repopulate the world and deal with the aftermath. Of course the levels of magic in the world are still pretty high. So there are still may Horrors left in the world. Though not so many as to make the world unlivable. May of the Horrors also left things behind to cause more pain and suffering even after they've left.
The game takes place mainly in the Provence of Barsaive. Though there are plans to release a book on Cathey detailing the goings on in what is now China and japan.
Barsaive was a provence of the Theran Empire(Think Rome with Magic, or Atlantis). Though the Therans would say that it still is a Provence. Much of the conflict in Barsaive is between the various kingdoms and city-states of Barsaive vs the Theran Empire. There's already been one war fought, which Barsaive won, but it's likely only a matter of time before another war begins.
Most of the "standard" fantasy races are there: humans, elves, dwarves, orcs, trolls. There are also a few "non-standard" races: Windlings, short winged humanoids, T'skrang, "lizardmen", though "dinosaurmen" would be more appropriate, and Obsidiman, rocklike humanoids born from living stone.
To start playing the new edition you'd probably want the player's guide and the gamemaster's guide. There's also two companion books, the player's companion and a gamemaster's companion. To get started you should only need the two guides. The companions deal with more advanced rules and expand the game. The next book that is coming out is I believe the Kratis book. It's a setting book detailing Kratis, the city of thieves in Barsaive.
That's all that's been release for the 3rd edition of the game so far. But there are the previous edition books too. While the exact rules have changed they can still be used as a reference. The adventures in particular can probably be used with relatively little reworking. Luckily since RedBrick is now working with a Mongoose, they should be releasing new books every at a relevantly good pace. *crosses fingers*
If you're looking for more information I'd suggest taking a look the the Earthdawn page on Wikipedia if you just want a summary of the game,
Earthdawn - Wikipedia, the free encyclopedia
The Earthdawn page and forums on the Redbrick site,
RedBrick Limited • Raising Your Game
There are also several good posts on the rpg.net forums that are probably a lot better then what I have here.
-Kcinlive