Monopoly is a bad game. Monopoly is a bad game that people play. Monopoly is a bad game that prints money as if it had secretly shackled an army of gold-summoning leprechauns to its factory floor.
Monopoly, as a study in game design, is all about the difference between quality and the perception of quality.
We've all played Monopoly, right? I'm talking about the Parker Brothers game on the square board where you're buying property and charging people rent. The one with the fistfuls of paper cash and the little plastic dog.
Yep. It's a bad game.
What does Monopoly do wrong?
The game uses an unfeasibly large amount of paper money that players are forever having to pass around the table. You spend as much time adding, subtracting, and making change as you do actually playing the game. To make matters worse the game regularly uses the concept of "ten percent" just to make things that little bit more complex. Admittedly, to some extent the accounting is the game, but I can't help but feel that the satisfying feeling of passing cash around the table could have been retained without turning every player into a mathematician-slash-retail-clerk.
One way to do this would be to standardise the denominations. Remove the $1, $2 and $5 notes and have everything come in denominations of $10. You'd have less change-making over trivial amounts, less game components to sort through, and the maths would be simpler throughout. (You could just as easily deflate the currency and remove the $500 note but (a) humans find big numbers and multiples of 10 satisfying and (b) the big numbers are part of the flavour of the game.)
Slow resolution / exclusive victory condition
A game of Monopoly is decided in the first three passes around the board (often even sooner). After that point the relevant property has been bought, and, barring some truly unlikely dice rolling, the rich are only going to get richer and the poor poorer.
Despite this, it can take hours to actually meet the victory condition in the game. The victory condition is, specifically, to be the last man standing on the board, so you're not winning so much as being the last to lose. Losing is based on running out of assets, and there are relatively few ways for wealth to leave the table, so with each player bowing out everyone else tends to become comparitively better armoured, making it take even longer until the next elimination.
The game should instead declare a victory condition of a player accruing a total of X cash, or being the first to build X hotels. The rulebook does include two alternative victory conditions; one finishes the game after two player bankruptcies, while the other sets a real-world time limit. These are both sloppy solutions to an easy problem. Victory conditions should be based on specific criteria, they should be individual (ie contingent on the success of one player rather than the failure of others), and they should be easily and quickly achievable as soon as any player displays a clear and sustained edge over their competition.
Jail is just not fun. It might be an icon of the game, but there is nothing exciting about being arbitrarily removed from play for one to three turns. If the element was going to be included in the game, it should have been tactical - contingent in some way upon deliberate player actions.
Mortgage and bankruptcy
First up, mortgage and bankruptcy are just not fun words. Playing a game about mortgages and bankruptcy is not inherently entertaining. Secondly, the rules for both of these parts of the game are complicated, slow, and heavy on accounting. No surprise, then, that these are the two most heavily house-ruled aspects of Monopoly, at least in my experience. It seems everyone I've played with has their own custom way of handling these situations, and almost all of them are better than the game as printed.
An example of the problems with these rules: you can avoid bankruptcy by selling swathes of your property. This is a losing move - you don't recover from selling property in Monopoly. The rich will get richer faster, and you, without a source of income, will get poorer faster. You're still losing, but not straight away, so the game has been unnecessarily prolonged while you continue not having fun. The rules for bankruptcy use, in one paragraph, the terms "one-half", "10 percent", and "principal", which really makes the whole thing sound more like tax law than a family boardgame.
Few meaningful choices
It is always the correct choice to buy property when given the opportunity. It is always the correct choice to build houses once you can. The only meaningful choices come in trades with other players, and trades are easy enough to assess that two good players won't enter into one as both will only offer deals that advantage themselves over the opponent. A lack of hidden information makes for poor trading gameplay.
What does Monopoly do right?
It's fun to play with the Monopoly pieces. Bundles of fake money, tiny little houses, title deeds to property and so on make your accrual of assets feel very real and immediate. You can see and hold your successes.
Monopoly wouldn't be the same if you couldn't be a dog, a cannon or a top hat. These icons have little to nothing to do with the gameplay, but they give players a way to express themselves. Everyone has a favourite marker (I like the top hat), and if you've played with young children the idea of "being the doggy" is disproportionately likely to lure them to a game that otherwise has "grown-up banking game" written all over it.
The Monopoly board is bright, clean and distinctive. It's full of primary colours, thick black lines, and iconic cartoons. The board suggests that things in this game are easily understandable and clearly delineated.
The "if only" moment
Humans assess long odds poorly. The hotel on Mayfair happens late in the game, rarely gets landed on, costs a lot to set up, and by the time it gets triggered is unlikely to really upset the apple cart. But the penalty for landing on the Mayfair hotel is so big that rookie players will quite happily descend into bankruptcy while claiming that if only someone had landed on the hotel, everything would be different. The "jackpot" is akin to the "shoot the moon" scenario - the highly unlikely situation that, if achieved, would turn defeat into victory. It doesn't need to ever actually happen - it just needs to be clear that it could. People love these things.
Fast turns, interactive turns
Turns go by quickly. You need to pay attention on other players's turns as you can only collect rent on your properties if you notice someone landing on them. This keeps everyone at the table engaged in the proceedings.
None of Monopoly's successes make it a good game. The gameplay is, objectively, broken. What it does do is make the process of experiencing that broken gameplay as enjoyable as possible. This makes it an attractive game for casual players, who will be able to enjoy the novelty of the setup for at least a couple of games before they realise its deficiencies. It also makes it a good game for young players, who aren't able to interact with a game on its competitive level but are able to use it as a tool for imaginative and social play, particularly in conjunction with older players. (Monopoly is also pretty good for kids who are at the right age for learning addition/subtraction math.)
Monopoly is not a good game. But it is a good product. It sells, and to some extent it sells deservedly (although it continues to float on brand recognition far more than on its inherent worth). If you have created a game which is, genuinely, a good game, you should probably spend some time looking at Monopoly to work out how to make it a good game that sells.
BONUS POINTS: If you made a list of why Monopoly works (which I just have), and then made a list of why World of Warcraft works, they would be, largely, the same list. Not coincidence.