I played couple rounds, very nice descriptions of enemies, turns out I'm gay and you're the CIA schizo, I guess.
As a deck builder n00b I had some gripes at the beginning but got "most" of the mechanics. It's not entirely clear at the beginning what the cost of mana is and how much mana we actually have. I think that "not enough mana" prompt should be accompanied with additional graphic showing where the mana actually is (now I know it's the blue crystal but at the beginning it can be anything) .
Similarly at the beginning I couldn't place anything on the playing field, which I found odd. I also didn't know what arrows do, by trial and error I figured out you can attack specific cards with them, but the first one I placed was bugged and I couldn't attack anything, was constantly teleporting back to my hand. Explanation for weapons could be also beneficial, you can't attack with your main card unless you have a weapon. I was surprised to find that green attacking border, started second-guessing myself if it was active before? No, that's the weapon card.
Regarding balance, when attacking archer with my archer both units died. I'd expect that the one attacking will survive, otherwise there's no incentive to attack units that can kill you, it's better to attack the boss card and let enemies attack your card (unless enemy decides to attack your main, then whoever has more health wins, yay!).
There were turns when the enemy wasn't playing any cards, then when he was about to die he decided to place 4-5. I unlocked new packs with cards and I couldn't go back from the chest screen - I could click OK and then I was still on the same screen with a locked chest. It was empty so I couldn't click it anymore and there was no way to go back.
Deck submenu is a mess, maybe because of my screen as I was playing it in 1366x768, I guess you can make a custom deck but since I couldn't unpack other cards I didn't bother.
In conclusion, you need explain, explain, explain. When picking up cards show where they can be placed, when attacking add small text over the arrow that says 'attack", when you have no mana highlight where mana actually is. You might also want to replace visuals and audio, right now it feels like a mobile shovelware.