The JoH spirit revelations confirm that the rules about spirits, demons and gods are a lot murkier than modern/civilized Thedas thinks. It opens the gates even more than core DAI that spirits=demons=gods by literally showing you how the Old God may have come to be. Like Hakkon, they may merely be highly evolved spirits that are bound to beings like a High Dragon. Hakkon even talks to you and I doubt vocally, since High Dragons don't have that ability. Reminiscent of how Old Gods communicated with Magistars.
That's only one major story revelation in JoH.
The other main plot point is just how tragic the world became in under one generation after the disappearance of Ameridan and the death of Emperor Drakon. The implications being that had Ameridan been powerful enough to defeat Hakkon, his next mission was to return to Drakon, help in gaining the assistance of the Dales during the Second Blight and have the full power of Southern Thedas fight in a Human/Elven uniting alliance.
The Second Blight would have been much shorter. Human angst against the Dales would may have been replaced by goodwill, forming a potential bond between Orlais and the Dales that would have prevented the Second Exalted March. With a Dales alliance Kordillus II may have never lost the Anderfels and other lands, if he and his father were able to spend more time maintaining the Empire rather than fighting a 90 year Blight. Meaning the Game may have remained dead and the empire less corrupt. Orlesian power and influence could have been focused on northern lands instead of subjugating elves and eventually gaining/losing Ferelden. The Chantry may have been more tolerant and less militant too, possibly being the Chantry that Leliana or Cassandra dream of creating as Divine way before their time.
Basically everyone messed up after those two historical figures were gone leading to the messed up modern Thedas of today. Orlais, the Dales and the Chantry had a chance to create something great and failed without the combined leadership of Ameridan and Drakon.
JoH also had some interesting insight into Tevinter's expansions south and their gods.
So there was a lot of lore and story in JoH regardless of being an open world map. I'm guessing this new DLC will be akin to DAO story DLC. Designed more like a dungeon crawl with a more linear and focused storyline. If the story is good then critics of JoH being an open world zone should be happier with this one.