The first time I played this game I lost after the first few waves but the second time when I played it I finished the game. To be honest the game is really amazing, I enjoyed the experience a lot with the combination of tower defense and card games, I can't believe that your team made this amazing game in only 48 hours.
If I have something to say about how to improve the game, after the first or second level you don't feel challenged enough or scared about being damaged, I think that the game can be more challenging to the player if you introduce some enemies who can make the player feel a little more scared about that and incite him to change the strategy (as example, maybe an enemy who appears on the other side of the map,but with low life, so, the player has to not always put the defense towers too close one from the other), also, this problem of challenge sadly made the heal card a little useless, so if the game feels more challenging the card can be a essential way to survive while the player is changing the strategy.
If you are thinking about keep working on this game after the jam, I wish you good luck :) .
P.S:
Talking about the game feel, the game feels so good with the laser, blaster and explosions sounds, the particles feel great too. And there is a little bug in the background of the third stage (it seems like it sometimes blinks).