I have seen this complaint too often and I would like these pompous game critics to enlighten me. How would you make the game non linear when the whole leveling experience is based around the class story. Yes other games have offered more choices in the leveling path but none of them to my knowledge had even a fraction of the personal story swtor has.
The most common comparison is to WoW and having spent more of my life playing that game than I want to admit, I found it refreshing to have the class stories central to the leveling experience. If you can't stand the linear constraints of the storyline, please do us all a favor and just stop posting because it is integral to the game and likely won't ever change.