I already answered to the question earlier, but I wanted to mention about one fun method I figured out, though it might work better for films, but I think it could be used games as well if tweak it a bit. It's a method to "craft" ideas, I call it simply Harmony-thinking.
When you're thinking a big scale plot, think of two words, one that brings you positive feeling, and another that has a negative feeling (more concretic the better) then think a situation, place, or a person with those two words in it.
Example: words Chocolate, and politics, what I got first in mind, was a dull office meeting and a man who gets a huge desire of a chocolate during the meeting, but can't get it because situation of the meeting is uptight and formal. That was a core of my short film I made, called Passion of Chocolate. (it's not yet ready because of sound editing is not yet complete)
You can also tweak the idea by thinking also the positive and negative ways of telling the a story, same words: Chocolate and Politics,
also gave me darker version when I was thinking a negative story, a Chocolate Dystopia, world where chocolate is gone or very rare, and the politicians and secret societies are the ones who are keeping the chocolate from everyone. Maybe even Chocolate Wars will be fought
The Harmony-thinking is simply based on thinking words that have positive and negative feeling in them and put them under a same context. It gives an instantly a tension to a story, which is maybe one of the most important things to keep any story interesting.
Another funny thing that this brings up is the word "tension" because it can also refer to electricity, and what it is needed to make electricity/energy? Positive and negative charges BD !
I think this only needs a bit of association skill, so that if a word gives you some certain of visual image in your mind.
I've been testing this thing for about a year and it still feels so fun to play with the ideas tweaking them as either positive or negative, results can be sometimes absolute silly, but sometimes I can get very deep story ideas too.
Moreover, I can actually use this to analyze other films as well, where I can find these two core words or "charges".
For example Akira Kurosawa's Yojimbo could be: a bad samurai with a good heart and bad samurai with a bad heart is put under the same village, (this is of course just the absolute core, and rest are built to beef the story to maximum hights)
My examples are though very movie related, but I'm sure this could work also to create game ideas or books. I think it's just a fun tool to add in the ways of making ideas.
(If you want to test my Harmony-thinking out, PM me and send me two words that has positive and negative feeling and I try to bring a story idea for you)