The initial reference point has to be to Knights of the Old Republic.
Before Bioware's role-playing game arrived, anybody who didn't sleep in Yoda pajamas was thoroughly sick with all things Star Wars. Between a string of uninspiring-at-best games and a couple of dreadful films, the galaxy that was a long, long way away wasn't long enough away for most. Then KOTOR appeared with a lot of style and even more vision and made everyone like all this lightsabre nonsense again, unreservedly. The universe had its romance renewed.
For the last half-decade, World War 2 has been similarly run into the ground. The grand conflict between the allied and axis powers is, in videogame terms, the biggest single licence that isn't actually a real licence. Make a WW2 game, and you've got an inbuilt audience, background, world-class character designs, interesting situations and probably the best villains the world has ever seen. But because anyone can make a game set in WW2... everybody did. It's got to the point where we feel as if we've done it all before. How many times have we crawled up the shingles of Omaha beach? If you added up all my virtual deaths in those bloody shallows, it's entirely possible that I've lost more lives than were lost in the real assault. Turn to the comments thread in any World War 2 game preview, and you'll see a string of people shrugging. Bored now! Bored now! Seen this before! What's next?