I really liked Railroad Tycoon 3. There are people who loved 2, that love 3 and there are many that really don't like it.
The 3d graphics are pretty cool and I spend lots of time just watching my trains. You still have the challenge of laying rails, placing stations, etc. In 3, you can also buy and BUILD industries, which is very cool. I've won some of the scenarios without buiding any track...just through building and buying industries.
The biggest differences are that micromanagement of cargos is no longer necessary and that cargo will move with or without your trains. Often, the best place for a depot or station isn't directly at the source of the goods, but in the path of the flow of goods....such as at the confluence of rivers, etc. That means that you generally have fewer branches and spurs to specific resource points.
The feature that most people love/hate the most is the removal of the need to micromanage cargo. The game will determine the most valuable cargo to carry to the next station automatically. You can still define which cars to carry, but it's harder to depot cargo or to build the familiar unit trains.