Test your driving skills.
Deliver goods in time without damaging truck or trailer.
Remember taking a rest or you will fall asleep and get a ticket.
Hit other cars, ignore red light or break speeding limit, you'll get at ticket.
Drive a truck with trailer at 140 kmh or more on the freeway without tipping over or getting damaged.

Don't like restrictions, just disable them in options.
Don't think the game it self is not enough, just install mods.
Don't think the mods are good enough, just make some with the tools provided by SCS with Blender for Free.

This is a real PC game with all the options you could want and a developer still updating with new features and fixes. :-)