The choice of blowing up or saving Megaton in Fallout 3 is often cited as an example of bad game design, but it's actually just fine. It is usually criticized for being not morally complex enough, being just a choice between being good or being evil for next to no reason, but this assumes the only role of a moral choice in games is to offer the player a neat little morality puzzle to solve.

Let's, for argument's sake, imagine an alternative FO3 from a parallel universe, where instead of it being a choice, it was just a normal quest of you saving a town from exploding. Maybe the guy even shows up to tell you to blow it up instead, but there is no way to actually do it. Wouldn't the experience of saving Megaton be lesser in this game?

Being able to destroy Megaton makes you saving it feel more meaningful, as a moral good only exists in relation to a moral evil, and making the choice real makes the game better.

It's still a pretty shit game otherwise, though.