People bitch regardless, they'll bitch more when a game changes too much from what it was. Example Gears of War series, 1-3 had plenty of bitching and still do but the series that made the biggest changes(Judgment)had the most bitching. Keeping what the game was meant to be is the most important part, if you can't do that its time to hang it up. Clearly opinions differ but mostly with fanboys, they either don't want to admit a game is past its prime or people say it is because they don't like said series.