Possibly the greatest modern game in existence.
It involves prediction, maths, construction, psychology, bluffing, deciphering, monsters, magic, and a host of other fun stuff.
Together they make a game where each time you play will be different, each opponent you play will be different, the meta-game is constantly evolving due to new cards and new ideas, and it can be played both casually and competitively.
The basis of the game is that each player is a wizard. You will have a deck of cards that you have constructed, consisting only of the spells, creatures and artifacts that you wish to use. Mixed in to your deck of spells are lands that you draw your power from, these enable you to cast your spells. You pit your choice of spells and monsters against your opponent who will also be using their own selection in their deck.