Well, initially I had big plans for gameplay, like upgrades and card penetration stats, maybe full auto too, but you know how it is , I spent the second day fixing bugs and polishing the game. I didn't really have time for that, but I appreciate your kind words, and I'm really glad you liked what you liked.
And about the boss room... well, I'd say it does need some balance patches xD and there are more ways to cheese the game. For example, you can still shoot cards while the game is paused, dead-eye style. It's a bug that I left because it is fun and looks cool. I'll maybe fix these in the future, maybe never, who knows.