There are five tiers for you to play through which as you probably have guessed, get harder as the tier progresses. It is pretty impressive how many bus routes there are for you in Bus Driver.
It sounds boring as hell I know, but it is more addictive than you would think and trying to drive like a normal and good bus driver is way more challenging than you would think. If you drive like a maniac, miss stops, break to harshly and so on, chances are you will fail and have to try again. You manage this and you are doing good and can progress in the game. It is so, so tempting to just drive really fast! But your score will go down. Instead, you have to stick to your route, drive in a proper manner and make sure you hit all of your stops. This is not Crazy Taxi! By that I mean you are not going to be hauling ass over the sidewalks, grassy areas and so on to get people to their destination as quickly as possible. The overall goal of the game is to complete your route in the best way possible.
If you have ever wanted to drive a big bus around the USA, this could be the game for you. I feel that it lays somewhere in between just being a game and also being a simulator. It seems the gaming world does not care about that and the game is actually labeled as one. While the folks behind Bus Driver have always made it quite clear that this is not a bus simulator.