The armor mechanic is a bit weirdly explained at the beginning (all upfront, too, and not re-explained unless you relaunch the game), so I fumbled a lot during my first couple attempts without even a good udea of why I died or how close to death I was. "Shield break: 3" isn't the most intuitive thing unless you actually understood how armor works.
Would also have been nice to have the damage and healing values in the card tooltips, since it's easy to forget when dealing with the face cards.
Once you get past that learning curve and realise you can leave the healing cards you don't need (so they show up later) by escaping a half-cleared room, it's actually rather easy, but a pretty neat game nonetheless!