First of all, if you do own Euro Truck Simulator 2, don't bother this game - it's almost the same game but worse. And if you are going to pay full retail price for this game, buy ETS2 instead.
Scania Truck Driving Simulator was made by the developers who made Euro Truck Simulator 2, which is a good thing. The game itself is really great and totally worth the price, but that's because it's almost the same game as ETS2, same map, same vehicles (but only the Scania ones) and same graphics. What I've seen, there's no story mode in this game, unlike ETS2 where you can start like a freelancer make your company growing until you have several employees and trucks. However, that's not how this game was supposed to be either, because then it would have been exactly like ETS2 -but worse.This game though, have some good game modes, including multiplayer and a wide range of tasks. For those who just like driving around, there is a free mode where you can just drive around and do anything you want.
At last, as I always do, I recommend this game to the players with a WHEEL, as in my opinion, all driving games are boring with keyboard and mouse. BUT if you do enjoy this kind of games with any kind of controller - don't care about what I think and buy the game.