Often I say my least favorite is Assassin’s Creed, but I only played one game in it. It was Black Flag, and while it was good, I can tell I would hate all other games in the series since the best parts were when you did anything but assassinating.
But I have extensive experience with Far Cry, and it is my least favorite game franchise if for no other reason than because it’s a formula that could be amazing, but Ubisoft has completely squandered it. It’s funny how Far Cry 2 is one of my favorite games ever, and yet it’s in a series I despise.