I love this game so much. I know it's just a prototype but god knows how many hours I spent in this game. I especially love to play it as a frostmancer with every single negative charm enabled. Because of this, my perspective on this game might be skewed a little.
The music, sounds and even graphics (despite being unfinished) are good. I have no complaints about them. The gameplay is extremely fun but not without it's flaws.
Many of the cards are underpowered. As in, there's no scenarios where using them is a good idea or there's a direct upgrade. Fixing them, I think, is essential for making the game more consistent, especially with a lot of negative charms enabled.
Deathly Fumes - the only case when this card is more viable than Poison Strike is if and only if the enemy has 2 poison, which is impossible without 2 Poison Strikes or 1 Super Poison. Only in that ultra specific case it's unique gimmick can even be noticed. Make it so that it triples the poison instead. It would still require 1 card to be good but at least the hights would be easier to reach.
Dagger - completely outclassed by Echo Potion or Echo Strike, which are more reliable shield breakers. Even if it did 3 stabs I'm not sure how effective that would be. With 1+2 damage or no cost this might become usable.
Strengh Boost - Strength potion is indeed easier than push ups. I see no reason to use this every time when you can just use the strength potion once.
Quick Punch - Fatigue is way too strong of a debuff, especially for non-ranged attacks, which become obsolete when "Explosive" charm is involved.
Meditate - powerful if you have enough energy to play it, but with "hesitation" charm this card becomes actually unusable, and with "hand pain" - borderline useless.
Teleportation - same problems as meditate.
The Bishop - technically fine, but the fact that this card doesn't do even a single bit of damage annoys me to no end, because all other chess cards do damage and look like. Make it do at least 1 damage. It won't be as offencively powerful as other pieces, but it would be consistent with other pieces.
Also, I'm very scared of the "Relentless" charm. Considering how hard the game can be with all available charms this one might make the game borderline impossible (this is not substantiated, I'm just guessing).
The crashing is a frequent but negligeble problem.
Overall, 9/10. Imperfect, but incredibly fun 100 plays later.