I think the game would be fun if I knew what was happing. It seems to be an arcade shooter-style game where you get random perks/buffs (I assume that is what the cards with different graphics are). I would recommend giving the player info on what the perks do and how they affect the player. Well playing I also couldn't play for too long without the cards popping up and stopping gameplay so I would recommend making the threshold increase based on how many upgrades you have.
The game controls well but I don't think there was a difficulty curve of any sort. You could make it, so the enemies shoot more often and make less of them increasing how many there is the longer you play. I think the game could be a lot of fun it is just lacking a few things to make the gameplay clearer and more satisfying to play.