Sid Meier's Railroad Tycoon

The Good
Freedom of action - once the basic features of a scenario are set (random resource locations, player-chosen difficulty level), it's all up to you as a player to decide what to do - which cities to connect, what locomotives and cars to use, what cargos to carry, when to borrow and pay back loans, when to buy and sell stock, on and on.

Building something - it's like a construction set or model railroad. It's satisfying to start off small, have it work and then make it bigger.

Replayability - once a scenario (100 years of game time) is finished, the immediate question is "could I do better?". And it's always fun to try. The random resource locations make each scenario sufficiently different that it really does feel like a new game (so you can't simply make the same decisions you did before), but not so different that you can't use general techniques you've picked up.

The Bad
Copy protection - when the game first loads it shows a picture of a locomotive and asks for its name. All the pictures and names are shown together in the manual, so you have to have the manual (so presumably you have a legal copy). But come on, it's over ten years later. The game hasn't been in stores for years. The company isn't making any revenue off of it in any case. Why do we still have to deal with this?

The limitation of 32 - you can have at most 32 trains running at one time (but I want more!). You can have at most 32 stations on one railroad (but I want more!). Once you reach these limits you can't make your railroad any bigger. Past this point the only way to increase your wealth (ie., your score) is to play the stock market. In one sense that's the most effective way to run up your score, since as time goes by the stock market valuation of your railroad can exceed its yearly operating revenue by quite a large margin. But after several years (real ones, not game ones) I ran into the final limitation of 32 - a railroad can have a maximum value of a little over $32 million (probably $32,768,000). Past that point the value is interpreted as a negative value, and the game abruptly declares that your railroad is bankrupt and you have "lost". And that is pretty much the only reason why I've stopped playing it - the "can I do better?" question has definitively been answered "No".

The Bottom Line
A game for people who like to plan and build things, who enjoy watching something grow and prosper strictly because of their own efforts. Not for those with short attention spans.

There are built-in limitations in the game (including one outright bug), but most players will never reach them without the performance improvement that comes only from long and repeated experience with it.