I see GLaDOS revealing herself early as a form of advancing the drama of the story to hook gamers into playing for a longer session. While the unreliable narrator does play a part, it is quickly established that the man (in this case woman) vs. machine plot device is used to give purpose to continue rather than the “because it’s there” design to complete a puzzle game. In the case of Portal, I think that the faster reveal actually helped suck people in their chairs because the gradual reveal is something that could be a detriment to video games because they are based upon instant gratification (press a button, something happens). There are exceptions, like RPGs which stem from pen and paper games which are different beasts altogether. Hope I didn’t ramble on too much!