Sequels of games like Call of Duty, The Sims, The Elder Scrolls: Arena, may come out every year or between 2 to 5 years or more.
So what is today's standard in animations, gameplay, features and so on?
And was today's standard, last years standard?
Do they repeat the same formula too much? Should they? If they change it too much will it feel as a sequel of the previous game?
Do old hardware of mainstream gaming devices hold some games development back as it's easier\faster\cheaper to produce new game for established mainstream gaming devices, thus creating very little changes for the game than just the theme and features?
Have we reached the peak of our imagination to produce something that has never been done before in features or size?
I guess the answer is different for each sequels.
But you should not compare the sequels of a game with another's game sequels.