If you're setting a game during the Cuban Missile Crisis, look through a library. find out what people were wearing, what other issues were in the news, how houses were furnished, what cars were being driven. Especially include things which now seem foreign.
Players very widely disagree with me about what's hard and what's easy. and in a way, 'I won, but it was a fight' is the best compliment a game can receive.
The most frequent complaint is that it's hard. True. it's a hard game to win Also, many people ask me how to use the secret debugging commands, apparently under the impression that I'll tell them.
If pushed, though, I'd say that the next stage will be reached when it it's no longer true that about 75% of the best games were written in 1980's on the way to that.