Thank you for playing my game and for your feedback!
I agree with all your criticism. I made this game a while ago in my second year of university so there's lots of stuff that could be improved on. The text visibility and scaling issues were caused by me not using Unity's UI canvas properly.
During development the Overlord was immune to the life swap card but this seemed to really annoy playtesters so I removed that. The shield cards are overpowered especially if you keep using them in the early game without attacking the enemies. If I get a free moment I will update the game to fix the scaling issues and to nerf the shields a bit.
Thanks again for your positive feedback, it means a lot.