Trading card games (also known as TCGs) combine collectable cards with a strategy game. You don't know what you'll get in a booster pack. You just start a collection and trade with other players to get the cards you want.
The best part about these card game is that they're always changing. You design and build your own unique decks, and each game you play is different. New sets are usually released a few times a year, and each new expansion brings new ways to stupefy and defeat your opponents.