Comment by jader201

In order of complexity:

- Thicket to Ride series: https://boardgamegeek.com/boardgamefamily/17/game-ticket-to-...

- Crayon Rails series: https://boardgamegeek.com/boardgamemechanic/2010/crayon-rail...

- Cube Rails series: https://boardgamegeek.com/boardgamefamily/18979/series-cube-...

- Age of Steam (with hundreds of print-n-play maps available): https://boardgamegeek.com/boardgamefamily/86/game-age-of-ste...

- 18xx: https://boardgamegeek.com/boardgamefamily/19/series-18xx

There are (several) other “train games” that are mostly one-off implementations with a train theme (often route/network building and/or tile placement, but sometimes not), but all of the above are families of several games that share a common system (components) and board game mechanisms, so once you play one, it’s often easy to understand/pick up on others in the same family.

The first, Ticket to Ride is probably the most accessible, and therefore one of the more popular options. But the others definitely offer a deeper experience, if you can handle the (increasing) complexity.