So far: Enjoying it reasonably well. However, I anticipate this will wear thin fairly quickly. Much of the fun of this game was anticipating all the plays your opponent could make, playing around them, and out-skilling them, or losing a hard-fought match and learning something.
The only times I've been really, truly frustrated with this game, nearly to the game-quittingly-displeased-point, was when I lost, and felt there was nothing I could have done, for reasons other than that the opponent's answers lined up perfectly with my plays. When the opponent RNGeapers into my best minion, into Grimes giving a Peacekeeper and a Blue Conjuror. Or they turn 2 (or even turn 1) flash flash (flash) Juggernaut. Turn 1 Zyx on mana tile, double Darkfire Sacrifice into Variax, etc.
This mode is going to amplify that. Aegis barrier on a ranged minion with killing edge? Do I have crossbones, or AOE sufficient to destroy the minion? No? I just lost. Nothing I could have done. Aegis Barrier on any value-generator, really, if I don't have tile-dispel or board-clearing AOE. And that's just one thing I've already faced off against.
I expect that, unless (manual) care is taken to prevent these game-breaking combos, this game mode is just going to degenerate into the most-complained-about form of solitare: Who can draw and pull off their broken combo quicker to win. Some may find this appealing. I'd rather play against my opponent, than race to draw better than them.
I already want Gauntlet back.