This is really impressive, looks like a full-blown commercial game. I played it for a while, but died in the area after the first boss battle, cause the difficulty jumped significantly, and I wasn't entirely sure what I was doing, so I'll agree that it needs a tutorial.
Main issue I had was the fact that as you keep getting new cards, old ones have a lower chance of being drawn(but I think it can be remedied by picking up the same card multiple times, haven't tried that yet). Also, the game was too linear, as you approach the boss battle, you have no choice but to fight, can't even go to a shop to buy stuff, but that's more of a personal preference.