Wizards of the Coast, 1993, 2 or more players, ages 12 and up. I'm going to go out on a limb and call this the greatest game ever made. It was the first of the collectible card games and spawned an entire multi-million dollar industry. When it hit the scene in 1993 I never saw anything like it. Local gaming stores literally could not keep the cards in stock. My friends and I snapped them up so fast and in such quantity we started calling it "crack for gamers". The concept is fairly simple- instead of a game ruled by a "rulebook", you have a very short set of rules that cover the basics of the game, and then each card has rules of its own written right on the card. I've read that the old Eon/Mayfair/Hasbro game of "Cosmic Encounter" was a major influence on the designers of Magic (another game with a basic rule set that is then modified by cards within the game - "the game that breaks its own rules" is, I believe, how it was billed). In a nutshell there are three basic types of cards- land cards (which generate the "mana" necessary to bring the other kinds of cards into play), "permanant" cards (creatures, artifacts, and whatnot that stay on the board) and "instants" (cards that have some sort of one-shot affect and then leave play). Each player starts out with 20 lives. The object of the game is to use your cards to reduce your opponant's life total to 0 (or run their deck out of cards). What really makes the game unique is that once you purchase a collection of cards, it's up to you to design a deck with them. Certain cards work together better than others, and the player that comes up with the best synergy has the best chance of winning a game. With the thousands of different cards available, the possibilities for deck construction are infinite. WotC even sponsors a pro tour attended by the best deck designers (and players) in the world, all vying for cash prizes.
Since its initial release there have been probably a couple of dozen new releases and literally thousands of new cards. The game is continually changing with new rules and abilities being introduced all the time. In fact, it is this very mutability that both attracts and repels gamers. Almost all of my friends have sworn off the game because they got tired of trying to keep up with the neverending series of expansion sets. I stopped trying to keep up as well as far as buying hundreds of cards and building decks goes (who has the time or money?) However, WotC now sells 4 preconstructed theme decks with each new release along with world championship decks (culled from the pro tour) which allow me to continue playing the game every once in a while with the friends I have that do still play. Call the preconstructeds "methadone for gamers".