Awesome concept ! Very interesting idea, I really enjoyed playing your game ! The theme is respected, the gameplay is interesting and the difficulty curve is quite good =). The graphics were great (the thumbnail is really funny) and the general atmoshpere of the game is quite pleasant ! The music was not really fitting, but that's not a bid deal ^^.
It was a bit frustrating to see a card with a dice I don't have, resuting in losing life just because of randomness. I would have like to have *some* control over that, like being able to roll a dice to get another number (that would have a cooldown so the player cannot spam it), I think that would add some depth to the strategic aspect of the game.
The "= =" and "± ±" cards were, for me, the most interesting ones, because they give the player that layer of control that normal cards lack. I would have loved more cards like this ! Give me other cards like "greater than", "lower than", and some crazy combination, like "= = >", "± ± <"... That would be amazing =D ! You wouldn't need the "roll" mechanic I said earlier if the cards were more like these (with a ponctual "numbered" card, that corresponds to numbers you already have, so you would have to re-think the mathematical ones).
The UI was a bit tedious to use at times, I would have liked to just drop a dice on a card instead of precisely having to aim for the corresponding slot ^^'.
Don't get me wrong, I really like your game, that's why I would love to see some evolutions =). That's an amazing idea and I had a blast playing it =)