An excellent game.
Let's start with the graphics. They are simply amazing. When you have the full graphics setting, set to the max on every option, with full-screen anti-aliasing turned on, the game looks just about as good as if you were staring at a train yourself. The smoke effects (both from brakes squealing and your train starting up) look just as good as the trains themselves. Trees, buildings, cars, distant mountains; they all look wonderful.
The cab's look great too. Almost every control you see you can activate, be it the bell, horn, throttle or brake. There are working gauges as well, and the speedometer accurately represents your actual speed. Brake pressure, throttle level, electricity (electric trains only), etc. Everything works.
The learning curve is steep, which means you will get a lot of replay value out of the game. Just try driving a Flying Scotsman (the most famous steam locomotive) and stopping it as need be!
The game comes with a track and route editor, so you can create your own crazy combinations of track throughout any of the locales the game offers you.
The game engine. Although it looks great, the minimum advertised requirements are a joke. The computer I first installed the game on was a P3 800 with a GeForce2 GTS, and at 800x600, it was horrible to play without having the options set to performance over graphics. If you don't have a powerful system, you'll have to sacrifice a LOT of eye candy to play this.
The activities (read missions) are a complete waste. Sure, they add to the challenge, but they seem to have been thought up at the last minute. Also, some activities take up to and including three hours to complete; who's going to play this type of game that long in a row?
The Bottom Line
If you enjoyed the other Microsoft sim products (Flight Simulator, Combat Flight Simulator), you'd probably like this too. But be forewarned; the basic concept is drive, stop, pick up passengers, drive, stop, drop off passengers, and follow the posted signs.
To all others, it'll probably seem boring unless your a train enthusiast.