A few, but I'd really like to get on a soapbox here really quick...
*steps up* Ahem.
Games are no longer simply about challenge. They are experiences. Artistic works intended to invoke emotion through an interactive narrative. That goal is no less valid than the goal of challenging the player, and sometimes there is value to using the "final boss" for something other than a challenge.
Consider games like Shadow of the Colossus and Red Dead Redemption, where there was gameplay after the "final boss" with immense emotional impact. Consider games like Halo: Reach or Crisis Core where the "final boss" is your character's final stand, and you are destined to lose (not spoilers, since both are prequels; if you know enough to play those games anyway, you already know how they end). Consider the first Halo, where the last bit of gameplay was not really that challenging, but was one of the most thrilling things a video game had ever done at the time. Or consider Modern Warfare and its sequel, where the endings are intense precisely because you can't do anything about what's going on, and only at the last second do you get to perform the one action that can ensure victory. These are how video games, as interactive narratives and impacting artistic experiences, have a perfectly good right to end. It's not challenging, but it sure is the intense emotional climax of the game. And there is absolutely nothing wrong with that. In fact, I'd say that's where Bioshock went wrong; its boss was just an excuse to challenge you a bit at the end, and it turned out not only easy, but meaningless in the relation to other recent events.
My point simply is, it's okay for games to feature an easy final boss, or no final boss at all, if they instead use that place in the game to provide a satisfying climax to the game regardless of challenge.
*steps down*
That said, some of the mentioned games definitely failed. As I said, Bioshock's final boss was the only part of the game I was actually disappointed in. Fable II is actually questionable; I like the idea of just letting you enact simple justice, but if you wait too long and someone else does it, you get kind of annoyed. Though that is a rather interesting way to do it, and I didn't hate it once I got a chance to really think about it.
