This looks like an interesting game with good artwork and music. It's a bit difficult to get started though. I didn't make it through the first match. Here are my suggestions.
1. Have an arrow indicating the object above the first opponent is the card he's referring to. I kept looking for the "card" and almost stopped playing because I thought the object above him was just a placard for his character.
2. Get rid of the timer, at least for the first few matches. I didn't even have time to read all my cards before the timer passed.
3. I get the marbles, but I need a better explanation of how to earn points.
4. Launch with an optional tutorial that tells which cards to play from your hand and why they're the best play for that round. That will help new players get the hang of the game.