Baldur's Gate wasn't very linear because you could travel from map to map of your own free will, in almost any order. There were some areas you could not access until you had satisfied some plot piece, though they were rare.
Baldur's Gate 2 was linear until Chapter 2 where it branched out hugely, overwhelming many players. But after Chapter 3 the game returned to being as linear as it was in the very beginning.
DAO offers nothing but linearity.
There aren't many non linear RPGs, but most notably are Morrowind and Fallout, where, if you like, you can travel straight to the end, and even defeat the game.