Narrative-wise, this is probably the single biggest source of facepalm-worthy moments in video gaming history. Someone already brought up Mass Effect 3 on the YouTube comments, but I want to reach for something else - Remember Me. This is a game which, by the strength of its setting, narrative and characters, promised us an interesting and engaging world filled with unusual technology and a society changed in mind-bending new ways. It gave us a protagonist whose entire plight seemed to revolve around the ethical quandary between freedom and security, between righteousness and collateral damage. It outright promised us the ability to rewrite people's memories and alter their personalities drastically.
I've seen games that have a sequence where they lead you somewhere, only to have nothing there. I recall a lot of The Legend of Zelda games that had this, as well as the Capcom SNES Aladdin game at one point.
This basically feels like something that's in a lot of games since, well, a lot of games aren't that well thought-out... which isn't to say that they're bad, they just have a lot of things that no one really thought about or looked at and said "we'd better put something here". After all, it's easy to overlook something that someone else catches onto.
So I'm working on a game that's basically a high scorer / rhythm game, but the theme lends itself to some moral decision making. I happened upon an idea last night where one could get offered a higher score in return for morally questionable behavior. And thought - why don't I just leave it at that?