SW:TOR takes place 3500 years prior to the movies. It's a conflict between the Galactic republic and the Sith Empire and you have to chooose what side you're on. Then you have to choose between four races and four classes, pick a name and enter the Star Wars universe.
The controls and fighting mechanisms is very similar to World of Warcraft. What is unique for this game is the storylines. It feels like the developers really have gone the extra mile to provide for interesting plots. And all the missions start with fully animated conversations that give alot to the feeling of the game.
And then you will get your own spaceship, and you will own a robot, and there is space fights, light sabers, cool gadgets and plenty of aliens. You will probably waste alot of time on this, but you will at least have alot of fun while wasting.