I enjoyed this, finished all the levels. Very straightforward, don't think it needs any explanation at all really. Controls are good except that the pieces that split into two tracks can be a bit finicky to get facing the way you want sometimes. Jeeting away pieces is great. A quick restart button could be nice.
The only thing that annoyed me really was the map being to small for some of the later levels and having to pick up every piece individually because I had started building in a way that I ran out of space. Maybe a way to pick up and move the entire track, or having a larger map.
Not sure how much longevity it could have, perhaps it would get work just fine with more different pieces. Some sort of obstacles you have to build around, already placed pieces of track to account for, having the train do jumps, etc.
I don't know how much far you want to take this, seems perfect for a mobile version at least. The graphics are fine and to the point, I think it could look really cool, and "comfy", with elaborate tilt shift type aesthetics and building around small towns and the like.