Do you remember how Calvin and Hobbes, in the classic comic strip, used to play Calvinball? They'd basically make up the rules as they went, changing them at whim and having a blast in the process. While you can't make up just anything on the fly in Fluxx, this popular card game does give you the ability to change the rules and even the end goal as you go. With its unpredictable nature and great card variety, Fluxx makes an excellent game for parties and large groups.
Everyone starts with three cards, and there is one basic rule: draw one, then play one. But that changes once someone plays, say, a "New Rule: Draw 3" card. Then, all players (including the one that just played that rule change!) draw three cards each turn, until the rule changes again. All players would still play only one card, though. That is, until a "New Rule: Play 2" card shows up! As you can tell, gameplay gets pretty crazy.
The game also starts out with no Goal, until someone plays one. Usually, the goals require players to have played a particular pair of Keepers, or cards with an object on them such as Bread or Chocolate, in order to win. Finally, there are also Action cards, which can be used to steal or rearrange Keepers, recycle cards, take extra turns, or the like.
Games of Fluxx often produce lots of laughs as New Rules pile up, players find themselves under strange restrictions such as limits on Keepers or cards in-hand, or a ridiculous difference between the Draw and Play values creates a glut or shortage of options that is just as easily wiped out again. Because of all this variation, Fluxx can take a little getting used to, as players must go through a few games before understanding all the cards' effects. A minor irritation is that it's impossible to tell how long a game of Fluxx will take. If the right cards are dealt, it's possible for someone to win before everyone has had a turn, and if not, a well-fought game can take forty-five minutes to an hour.
Still, the idea at the core of Fluxx is simple enough that anyone that can read can learn how to play and enjoy it. All it requires are the deck of cards, a little space, and anywhere from two to a whole bunch of players, so there is practically no setup involved, and the game possesses remarkable versatility and family appeal. I highly recommend it.
Fluxx and its variants (including Monty Python, Family, and Zombie versions) are made by Looney Labs, and can be found at many popular game stores near you.
Have fun, and never lose that competitive spirit!