I didn't have a hard time understanding the game after reading the tutorial. The visuals looks amazing and matches with the music and UI. I could definitely see this get expanded into a game with more card types which can add many layers of gameplay. I did also ran into a few small visual bugs like my mouse moving off from the card while dragging and also card disappearing when dragged to the right side of the ship. But overall I think it's great what you have made in 4 days!