The game system in The Moaning Words is practically identical to the legendary Triple Triad (the Final Fantasy VIII card game). Each card has four numbers, one on each side. When you put a card down, if the number of one of the sides is higher than the number on the adjacent card, you'll flip it over and conquer it. But obviously if your opponent then does the same, then she can also conquer your card.
As you win games (honestly, a pretty difficult task), you can unlock new cards. At the beginning you have some really bad cards, making it really difficult to win, but gradually you can put together a deck of relatively good cards.
The Moaning Words is a pretty entertaining card dueling game that offers a very simple gameplay and an exciting atmosphere. Plus some of the illustrations on the cards are really outstanding.