When I was a child, an Xmas tradition in our house was that the whole family would play Monopoly. It was a fun game, even though my father would always win. It seems they played it so much in his childhood that he still remembered all the rules and cards and prices and so on by heart, thirty years later.
Me, I wouldn't remember what I did yesterday, if I didn't have my ikiwiki-powered journal.
Anyway, in a random discussion with my SO, we thought of some variants to the rules that might make it more interesting to adults.
First, introduce a legal system, with lawyers, law suits, judges, etc. For example, if you don't want to pay your bill, sue the landlord for something. This would give some time to go on with other activities. The winner is the person who first throws a double, and the loser pays 1d6 times the original amount. (Exact rules to be determined by playtesting, of course.)
Then introduce a political system into the game. Let players or bystanders be elected into a parliament, which gets to invent new rules.
And finally, allow politicians and judges to be bribed. Corruption is rampant in the real world, so it should not be missing from Monopoly, either.