Gamasutra - Linearity: A Necessary RPG Element?
Gamasutra has a piece called Non-Linearity: A Necessary RPG Element?, which takes a fairly shallow look at linearity vs non-linearity in RPGs:
I have often noticed that game reviews mention that the game X is non-linear as if it deserved kudos for that alone, or that the game is linear as if it were a bad thing. Is it really?
In the end, it boils down to the kind of game the game designer is trying to make. If the designer wants to take the player on an intense emotional roller coaser ride - well then the game has to be linear. You can't control what the player feels until you keep tight control on which places the player visits and in what order, which persons player meets and in what order etc. Even then it won't work for all the players.