What we have seen:
-the board is visually 3dimensional, but the cards remain cards and are placed on the board
-leaders are 3dimensional characters standing at the side of the board
-only 2 rows
-there are abilities with different effects depending on the row
-the number of mulligans depends on the leader and seems to be a lot higher
-the mulliganed cards stay at the side of the screen until the end of the mulligan phase
-no more silvers, because with the card cost system, there is no need for them anymore
-base strength is displayed on the detailed card information
And probably a lot more that I have missed or forgotten.
Honestly, I still can't give a real opinion about the changes. Most of the visuals looked great, but I didn't see enough of the 3dimensional board to get used to it and to tell if it really fits.
The reason for removing one row per side was stated as avoiding to have too much text on cards, if abilities for every row had to be described. With the shown content, I honestly say anything about that yet. We have hardly seen any of those new abilities, and haven't seen any actual gameplay to say how it works. At least the reasoning didn't sound too convincing.
All in all, the HC reveal seemed far too short and without any real gameplay, I don't see that much meaning in showing that video.
I would have preferred a written announcement with a full reasoning behind the changes. At least for me the delay to give us visuals didn't improve anything at all compared to an earlier anouncement without visuals.