Yeah, some of the terrain types are technically the same, from a gameplay point of view. Just to review:
- mountains, lakes, ocean : impassable
- hills : when you stand on one, you can see farther
- forest, plains, desert : normal
They do produce different resources (e.g. "rare plants" vs. "nomads", but those differences are only visible in tooltips. :)). I may make those have some different impact at some point.
Thanks for the feedback and suggestions!