The discussion regarding alternative gameplay made me think of LA Noire a lot.
If the game works as intended, then the mechanics of searching for clues and interrogating people will be as important to the experience and moment-to-moment fun as shooting.
Likewise for Deux Ex and the upcoming Human Revolution, where you can choose to gun down hordes of enemies, and deal with the consequences, or opt to sneak, hack or talk your way into and out of trouble.
Honestly though, I think until somebody manages to make a game where speaking and navigating through a conversation to get what you want or out of trouble is the core gameplay mechanic, I think we'll be stuck jumping back and forth between sneaking and killing.
There are books and movies that 99% dialog and 1% action, but maintain the entertainment and tension. Games need to make that 99% possible.