There are no series without the capacity to do wrong, but some exercise that capacity more than others. Ratchet and Clank has been pretty solid though, after a bit of searching through all the series I've played at least some of. I don't think there's ever been a bad Metal Gear game either, one that's screwed with the mechanics or been gimmicky. But Monster Hunter, Armored Core, Assassins Creed, Resistance, have all done things at some point that I don't like. But I still forgive them a little bit. Although Monster Hunter sends me into a murderous rage at the thought (CAPCOOOOOMMMM!!!) and Assassins Creed is gradually getting to the point where I won't buy them at all.
Oh wait, Portal has never done anything wrong in its life. More of a duo...logy but still.