It's not great that every single monster injects negative cards, when the whole gameplay is supposed to allow the player to master combos. You win by growing your ability to combo, and you're never allowed to combo well. You make sacrifices to get good cards, and then you rarely ever see them come out, much less TOGETHER.
Plus, even if you play the negative cards, they don't vanish, they're STILL INSIDE THE DECK after you tried to play them to get rid of them, which is UNLIKE all other punishment cards in other card games that are popular. The only reason for the player to use them is to try to complete a combo.
It doesn't make sense to lose HP for movement, when you aren't out of resources, and you CLEARED the past areas, so they should be SAFE again.
I don't like that a card can only get 1 upgrade, because 3-mana cards are ALWAYS too expensive to use, even if you upgrade them 1 time, because the player is always mana-starved, ONLY the cards that cost 0 or 1 are "affordable", but a 3-cost card requires 2 upgrades, which you can't get, because if you play a 2-cost card, you can't afford to create a combo any more, which you MUST have, for ALL monsters will basically defeat you if you miss creating a combo even once during the battle, or you'll have such low HP the very next monster will get you.
It's not at all clear what combos the monsters will resist, and which they won't.
The artifacts are great, but there could be more of them.
There are way too few interesting upgrades and cards.
It's not great that the map is so tiny, and there's only one big villain. Is he really a "boss" if there's only 1 level and the game is over? Why is there not a 2nd map? The maps are ALL basically railroads, not real discovery. 1 donut that leads to same place isn't real choice.
Just when it starts to feel like you accomplished something, it's OVER and you didn't even get to build a good PC or deck.