Saw the overview video, here are my thoughts:
-First of all, before i get to the gameplay part, i want to say its nice to see all this amazing leader card art return, but it sucks that we had them as premium when they were leaders, we lost them when they were replaced by 3D leader models, and now we'll have to get them in premium again... since they're all legendary, 12x800= 9600 MPowder, that's a LOT of powder for something we already had
-Its great to get new cards outside of expansions - Trivia: since HC started, on October '18, we only had 3 cards released outside expansions: Hemdall, shortly after HC started; and more recently Alzur and Madoc, before and after WotW.
Also, even better that they're buffing "weaker" archetypes like Pirates, Dwarves and Vampires.
-Its funny that Slama talked about powercreep and how they wanted to bring weaker cards to the same level, on the first part of the video... then they go and introduce 12 OP cards (maybe not all 12, but most of em) and the reworked bronzes to combo with them, also really strong.
-Most of these 12 Legendary cards are really strong, and are engines you NEED to deal with or you most likely lose, like Kolgrim or Gezras. However, most of these are 7pts or more, outside of removal range from all bronze specials, and you only have one Heatwave (unlike NG which has Heatwave no.2 a.k.a. Yen Invo). This might be an indirect way to push locks to the meta even more, after last balance patch, i know i will be using Dorregaray+Faction Lock on most of my decks...
(EDIT) Also, i noticed most of these new cards have really long texts, i have to admit i had some trouble envisioning how they would work right off the bat. However i maintain my position most of them will be really powerful and will strongly affect the meta.