Mario is a good example. If you think about the number of high quality games that are either directly related to or spun off from the mustachioed plumber, they're only slightly dragged down by things like Luigi's Mansion, Mario is Missing and Super Mario Land 2 (ooo, controversial).
Similarly, Zelda. In fact, is Zelda a flawless, unbroken run of good games? Are there any other franchises like that?
And then on the opposite side of the scale, you have the likes of Resident Evil - about two or three good games and about 10 terrible ones.