Code 777 is a classic first released in 1985 (and recommended for a Spiel des Jahres in 1986) that remains an excellent representative of the popular deduction game genre. In this game, players are working with an imperfect information set, asking questions to fill in unknown variables in a hunt to deduce one's own set of numbers. What you do know is the numbers that each of the other players have in front of them; those are the easy ones to mark off on your sheet as not possible. Then things get tricky as you work to figure out your three tiles from the remaining 13 possibilities.
The one problem with the game is the method used for narrowing down your tile set. This is done by drawing a card and asking the question on it. Sometimes, though, this is not at all helpful as the question fails to reveal any new information. Turns drag on as you wait to draw a card that helps you narrow things down....and then another player draws that card and you realize that things are hopeless. You can take a guess, or you can go back to the beginning and modify the game. Consider some potential house rules for questions such as draw two and pick one, or even come up with your own cards with each one offering a selection of questions you might ask. Compared to other deduction games, the cards in Code 777 help things get started for new players, but they quickly become a limiter for people who just need one last question answered. Fixing this makes the good game a great game.