Hey,
Nice game, I enjoyed playing it.
I do have some tips/recommendations:
It would play much nicer if I only had to press the spacebar once and shoot something instead of needing to hold it and then just auto shoot. Taking damage could be more obvious by seeing a visual effect or color change, that's up to you. The music is ok but could be better.
It takes really long to get to the end, what I understand (it should be a challenge), but for the first (and only) level, it was too hard.
I like the way that you have to pick a card with an ability and play with that for the rest of game, but I think there could more in a different way. I love the art and think it really fits the game. I would only add a little bit more detail to the background.
For your first Ludum Dare, I think you did great.
I will rate it after the Game Jam is over.
Great job!