Well...I want to agree with Yahtzee. He usually has interesting points of view. So...I'll just agree partially.
As it has been said before, some sequels work. Mario 1, 2 and 3 are good, each one different from the previous and with both familiar and new elements. Even Mario World was good. I'll admit some other Mario games are not as good but at least those three worked back around the NES/SNES era.
Yes, some sequels are never meant to be, such as Tron Legacy, the sequel to a movie that no one knew of and no one asked for.
I also agree with the fact that fans don't know what they want. They usually ignore innovative and original games and go with the familiar and pretty. Portal is only popular because of internet memes that spread out (I know that's why I actually started playing it). Games like Call of Duty are pretty much the same. Hold on, fanboys! Let me finish. Although they have different plots (Somewhat), it's essentially the same. You grab a gun, you kill half of the world (Conveniently, the bad guys) and you have yourself a CoD game. I know what you're thinking: "Oh, but what did you expect from a FPS game?". Good question; I know CoD is a FPS and that the mechanic will remain the same. But I don't see the point in buying a new CoD next year when it will be more or less the same as the one I have right now. more maps, more features; it's still the same.
But at the same time, if you offer fans something new, they will rant about it forever. Case in point: The new Devil May Cry in development. I'll also admit I'm not crazy about the new Dante.
So no, fans don't know what they want. Developers should just do their thing and try to put little attention to what we say, kinda like when a parent is buying stuff at the market and the kid keeps bugging him about buying something. He keeps it in mind but not really.