As it stands now, BLAME has one "victory" condition and one "failure" condition. In the finished product, there will be a few different victory and failure conditions. These victories and failures will unlock Achievements which will help flesh out the story for those who wish to unlock them. Not only that, but certain elements in the game will be hidden away. These secrets will also unlock new pieces of the puzzle, but there's absolutely no pressure to find them (unless you want that ultra secret Achievement, or the super special ending).
Now, hiding away elements of the game might seem gimmicky, but I want to capture my favorite aspect of video gaming. Easter eggs, hidden features, unlockables, and all of the other secret stuff in gaming that has inspired the imagination. They won't be necessary, and the game will have a good amount of game content besides the secretive stuff.
There's another feature which I really want to implement, but I'm not sure that it will fit within this world. Since the world is still in development, I've still got some things to test out, but if it works out there will be room for some pretty cool features to be added on top of it. Until it's official, you might be able to find pieces of it in later builds, but if I said what it is right-out, well, it would defeat the secretive nature of the game.