Non-linearity as you see it means only one play through for me. Games that allow me to explore every nook and cranny on my first play through like Deus ex do not give me any reason to play again. I take my time, reloading a save now and then to try different things and regularly back track to explore each level whole. A second faster play through would only diminish that experience.
Less linearity is nice, but usually over 90% of the content is exactly the same in each play through. The Witcher 2 is a welcome exception with 2 separate campaigns in chapter 2. Fallout NV was pretty good too in the last hours of the game. But I don't restart from the beginning anymore. I keep a save game to go back to a decision point and play the other path(s) along side.
Just playing as a different class or with a different weapon is not enough incentive to me. Last time I did that was with DA: origins. I did 3 full playthroughs to play out all the different paths. Getting through the dungeons started to feel more like work then fun in the end.
Shorter more compact experiences are much more likely to get extra playthroughs. Half-life 2, portal, portal 2, uncharted series, all great fun to play through again multiple times.
Anyway both linear and non linear games can be great. Terraria and portal 2 were both great this year at complete opposite ends of the spectrum.







