There are few changes really. Although we could note that over the different editions, Malekith is portrayed increasingly more as a High Elf gone wrong, rather than the souce of evil. That role seems to shift more towards Morathi who's portrayed as a (generally negative) influence on Malekith.
Malekith is still bad, and terrible, and still instils people with dread. But there is a bit more room for his internal struggles, his attempts to build something and not just destroy.
Morathi is ever more pushed into the role similar of a cartoon devil (and seductress), whispering bad ideas into people's ears. Sometimes she's portrayed like a Greek godess of beauty, power, lies.
But nothing "really" different.
She does have one special thing coming up, as a result of the focus on Tyrion and Teclis on the High Elf side. She seems to have a thing for Tyrion, who is a mirror image of his great grandfather Aenarion (who she still loves, apparently).
I imagine this is to tie the story more neatly with Gav Thorpe's books on the Sundering and the Tyrion and Teclis novels.
Hellebron gets a bit more attention, showing her as a mentally unstable crazed old hag. However, within her insanity there is a never ending ambition and thirst for power.
The conflict between her and Morathi seems to have shifted to the background.
Overseas we're still raiders and slavers.
I think one change is the notion that Hag Graef takes a more prominent place within Naggaroth. I think in 6th, Malus Darkblade was still portrayed as a fruitcake roving the wastelands or being an army commander. Now he's risen to power and became the Drachau of Hag Graef.
His power and influence is growing, in spite of his condition, and it's clear his ambition is driving him to rise one more step in the echelon and to challenge Malekith.
With the books of the Sundering and the place Dark Riders are getting, we see the origin of the Dark Riders in more detail. They, apparently, were Raven Cloaks or something along those lines. It was an order, or caste, of messengers and spies forming a network which was employed during the Sundering. They also keep an eye on the cursed forests of Naggarythe in the wake of the wars against Chaos.
Hence, the feathers on their cloaks.
Black Dragons are still considered a twisted dragon, bred under Malekith's order.
Lokhir Felheart was a name never heard before 7th. He's one of two big Corsair Fleetmasters. I can't remember the other one's name.. He didn't get a lot of attention until the End Times.
The new units haven't really been given an in-depth lore introduction. Some of them are built on stories we already knew:
- Warlocks are male sorcerers cursed by Malekith. Before the 8th ed book, it was known that sorcerers would be forbidden by Malekith because of the prophecy that Malekith would be taken out by a male wizard. The unit of warlocks simply took it a step further, by cursing all male casters and condemning them to the life of Warlocks who need to feed on and sacrifice the life of their victims to delay their cursed end.
- Sisters of Slaughter are gladiators, coming from the fighting pits which were known to exist (ie: from Urian Poisonblade).
- Kharybdis are sea monsters, which were known to be captured by beastmasters and kept in the holds of Black Arks.
- Sourgerunner Chariot is considered part of a Beastmaster's arsenal to hunt monsters
Then there are the Bloodwrack Medusae and their shrines which are an entirely new piece of lore which never existed before. The paragraph long explanation for them simply notes they were Sorceresses once upon a time, too greedy for power and beauty, getting one of the Elven godesses angry and being cursed to that form of life.
They do have the ability to kills things by their "stare" which is why the Shrine has a mirror to ward the troops walking behind the Shrine.
The End Times conclude a lot of the plots and stories that have been laid out throughout various books. It's... interesting. But I won't spoil those