Cities: Skylines is a wonderful game, as evidenced by the many dozens of hours I’ve spent in it. That amount of game time has also made me discover some of its limitations, which I’m describing in this note. (Why, and for whom? Mostly for myself, using it for inspiration in case I ever get to work on a game like this myself. One can dream… )
The game comes with a handful of station assets (train and metro) which are not usable in all cases. There are DLC packs which provide extra station assets, but their connection directions are still predefined and not modifiable, which limits their usefulness.
One assets I’m missing in particular is a stacked underground station layout (Turmbahnhof in German) which greatly facilitates changing underground lines. Examples in Berlin include the U8–U9 exchange at U Osloer Straße and U6–U9 at U Leopoldplatz. These are tough to replicable in the game, and would need custom assets (I’ve not dabbled with creating custom assets yet. It’s not quite part of the regular game and is not trivial. ).
Many real-world stations are custom-designed/built to fit the needs of the situation. In the game, you only have pre-built assets. Transport Fever 2 has modular stations, but they’re also not as flexible (no Turmbahnhof possible, for instance).
To elaborate: Configurable depth of underground tunnels.