Hard but satisfying and beautifully executed. Deceptively simple, great progression and challenges. Really imparts something of the furious logistical chaos of underground rail (and some others, elevated, trams and shinkansen) across the world - with their own flavour and geography!
Cheaper in Google play ~£1.20, but available across multiple platforms.
*I mean I’m not very good, but I’m starting to develop tactics. Nice to see myself in the stats charts;)