Look the same thing is true with pretty much every piece of fiction from novels to movies to whatever. This year I've probably read 20 or 30 novels and seen many more films and each of them used a variation on a few basic plots that have been around for thousands of years. The sign of a great book or film is not that it tells a basic narrative that nobody has ever told before, but rather that it tells that basic story in a compelling way.
Games are much the same.
A good example of this is X-Com. X-Com was a brilliant game. Assemble, train and equip your squad of soldiers and send them out to do battle against alien invaders. I can't stand most real time strategy games mostly because the back story is so ridiculous its hard to stop laughing, and I have no time to learn all of the bizarre different units. AO2 works very well because it brings a well-balanced historical perspective that I can jump into immediately.