The answer is Balance. Not only the game, but the concept as well.
Balance represents the perfect mixture of excitement, challenge and learning.
Balance is based on the Eastern philosophy of Yin and Yang, which suggests that the universe consists of positive and negative forces and that good things happen when those forces are in balance. When confronted with Tetris-like pieces with imprinted words, the player must decide which side of a scale to place the pieces on to maintain balance. Each word-piece has a corresponding antonym that will fall some time during the course of the game. The players of this game will attain a high level of automaticity in recalling antonyms. Antonyms are traditionally learned through rote practice with lists.