I always wanted to try that.
Its pretty sweet. The hardcore dogged it because Sid made it simpler and brightly colored, as opposed to what PopTop was doing with the Railroad Tycoon series (ie, more realism, more trains). So far I'm messing with the Tabletop mode, which is pretty much like a big trainset so you can build and do whatever you want with no pressure or costs.
You get a home town that has a station and a little track. You build more track to connect towns and transfer goods between them. People, mail, paper, food, and just general stuff to move about. You also have industries that arent towns. A lumber mill cuts trees and produces lumber. Get the lumber to a town that produces paper and make money. Move the paper to a town that has a newspaper and make even more.
In SP you have AI (and theres multi but god I imagine thats slow) that is trying to do the same. You cant use rails that you didnt build. But just because you don't own the rails doesn't mean you cant make money off them. So your rival built rails connecting a lumber mill to a town that makes paper, you can buy the paper factory and make money off of it. Then theres new technologies that you can own that grants you a monopoly for 10 years. Is it worth it? Can you live without it 10 years (when it becomes open to anyone)? The idea is to eventually buy out all your competitors and rule the rails.