I can now think of two franchises with three solid films to them: the Bourne trilogy and now Nolan's Batman trilogy. If the forthcoming The Bourne Legacy is good then it'll be one helluva quadrilogy.
I think the Mission Impossible
movies keep getting better with each installment. That's the best quadrilogy I can think of. (Personally, I didn't care for The Bourne Legacy.
I think it demonstrated pretty clearly that the franchise has already said all that it could possibly have to say on the subject of condemning American super-spy/assassin programs.)