Hey,
I found a few minutes to play the tutorial levels and quite enjoyed 'em. A big turnoff for me though is the building interface. The manual task of selecting a tile, then picking a type of railroad to use in it, then rotating it to fit, all felt very tedious. Unfortunately the game's design precludes you from just moving the cursor to the next tile, since you don't necessarily know what that tile will be. Hrrm.
How about this?
Tiles are placed by selecting a tile type from the palette on the left, much like a tool in a paint program, and then painting them on the board. The mouse cursor should probably even change to look like the tile. This doesn't completely remove the problem, but it does mean that frequently used tiles like straights and corners could be painted in quickly.
It'd also be handy if corner pieces auto-rotated to match two adjacent tiles where possible, rather than just one.
I also found the interface design a bit manky at times, a good example being the post-game congratulation screen where it took me a while to find the close button. Most of the buttons could be bigger too.
After finishing the tutorial levels I opened up the first "real" level, thought about how annoying the interface would make it, and shut the program down

This game has great potential, but the interface is holding it back IMO.
Oh, and you really need to add sounds for every player input action. It makes a huge difference, especially in games that are all about clicking on stuff.