What are the key differences between the Steam and Age of Steam games?
- Anybody can ask a question
- Anybody can answer
- The best answers are voted up and rise to the top
Assuming you're referring to the "standard" version of Steam, the two major differences from Age of Steam are:
Smaller rule changes include tile costs, tile distribution, no income reduction, loco is not allowed if you're on 6 already, final scoring for tracks is 1 VP per link, and when shipping you can't give more points to any other player.
This great review contains a more detailed list of differences.