Monopoly is a wonderful game, BUT... Most people don't play it properly. Due to this, Monopoly takes too long and tends to cause tantrums even among full grown adults. If played properly the game is 20 minutes to 90 minutes. The faster speed helps a lot in mitigating the pain of having a bad luck game.

If you ever want to attempt Monopoly again, I recommend reading the rules first and playing by the rules as they are written. Majorly improves the game.

No House Rules. The worst house rules that have ruined Monopoly are:
1) Putting money for any reason on Free Parking
2) Landing on an unowned property and not Autioning it if no one wants to buy it. (Auctioning should be taught even to the youngest child, it is a valuable skill that most adults think is too hard for kids.)
3) Not charging the 10% fee when unmortgaging properties.

When played properly, Monopoly teaches a lot of valuable skills. Skills like Auctioning, percentages, and budgetting.

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I have played Monopoly in tournaments. Although I have only come in 5th place 5 times out of groups of 83+ people each time, I am confident in saying that I am an expert at the game.

I have seen people try to introduce various house rules in the tournament, each time they made the game worse (as well as the judge forcing those tournament games to be redone from scratch).