@caPnAhab the game has a notion of morality points with some more or less fixed 'fate' things, so if you play through and fight people more than you have to, or even 'rudely' keep your weapons pointed at them (there's a special command to holster weapons), it'll affect how the game plays out at certain points... allies come along or decline, the overall end which can be a tad bleak - russian game.
@caPnAhab hmm, I can't find the announcement anymore. I thought they were going to work together with the fan base to design new levels this time but now I only find articles that say it's very unlikely and Valve hasn't said anything about it.