The passenger system gives the driving a bit more consequence than usual. Forty people are sitting behind you, and a few ugly stops or clumsy turns can hurt comfort and cut into the money earned from a route. Different buses also have their own handling quirks, which makes switching vehicles feel worthwhile rather than cosmetic.
There is a decent business layer once the fleet starts growing. New offices, hired drivers and automated routes keep the company moving while you take the wheel yourself. The current version also has store content that normally costs real money unlocked, along with a healthier cash balance for buying and upgrading vehicles.