What happens is that very few people read the rules properly and make up their own. That makes the game go on longer.

The rules I specifically mean are dealing out two random properties to each player at the start of the game, and auction bidding. (Look in the book, they're there). When you land on a square you don't want to buy it IMMEDIATLY goes to auction between the other players. Also you use your turn to swap and trade properties or deals with other players.

If you omit these rules (as most people do) then the game goes on forever. Playing properly, with four or five players it can be over in an hour

BTW off topic but there is no such thing as "immunity" in the game. People need to stop that nonsense. Before we got hooked on poker my boys and I used to play monopoly quite often.