I like the overall game idea, execution is hit or miss.
Very confusing at the start. Why do you let the player "Start Journey", which sounds like "Start Game", when they don't have any cards? Just prevent that if you know it doesn't work! Almost feels like you're trying to trick new players.
The main gameplay loop is great, and I like the concept and general incremental design around it.
I like the visuals in general, though definitely could use some basic animations to help tell the player what is happening. e.g. show damage amount temporarily, not just resulting hp. showing that the player healed. showing your stats change when you change cards. when the enemy changes (especially if it's the same type of enemy) and other things like that.
Battle Results screen is obnoxiously slow (would be fine if skippable).
Progression is really really slow, i would have preferred it a lot faster. also related is stronger enemies don't give more, which feels bad. Feels too grindy in general. I don't mind some amount of that, but the time between meaningful decisions was too long most of the time.
Health card seemed to do nothing? i gave it to one of my creatures or used it, the card disappeared and the creature didn't gain hp, and neither did i
Music is nice, sound is mostly good, though battle sounds are pretty weak, and should be varied (based on enemy, and based on death or not)
I kept playing partially because i wanted to see what would happen when i combined two level 3 cards. instead of a nice big reward, you are very heavily punished as the player, by losing some of your best cards... without warning. oof.
Sorry for the long list, I did like it overall, and congrats on the project!