Nice little game!
Visuals are good, it all fits into its own theme very well. Inclusion of a small story also helps sell the game overall. Music also fits well.
The rules at the beginning definitely go by way to quickly, although it is pretty simple to pick up the game by playing, having the player choose when the text proceeds would help a lot with the first playthrough. Since I had no idea what was happening first time through.
I think that the timer may go against what might be the most fun of the game, which is looking at both players cards and choosing what to do. I think the timer is a bit too fast to make good decisions, and it dumbs it down a bit more to just > If high health -> attack, if low health -> heal. I think a slower paced game would allow a lot more opportunities to add more cards and create more meaningful and thoughtful interactions.
Nice job.