Indigo prophecy aka Fahrenheit did this style of game before, but without a known IP or writing staff.
The only problem with that game was there was literally only Simon Says mini-games, and the story went off the damn wall about 75% through. In a post mortem interview, the creator basically said they spent too much time on the beginning, and thought it would keep the players hooked. The intro was engaging, true, but it easily fell off as the story just got more and more bizarre.
edit: adventures game as a whole aren't new at all, but these style games have that morality option throw in, with branching story points based on decisions. a bit different.
A game primarily defines itself via interactivity.
The Walking Dead, while being a great experience, a good story, artfully told, heartwarming and touching it is by any standard a poor GAME.
Not because it doesn't have great qualities, but because of the fact that the game-play mechanics are so rudimentary.
I remember some of the old interactive movies from the 1990s...popular during the dawn of CDs. They were similar to TWD and were fun to watch but they weren't great games.
TL;DR: Great experience, bad game.
Games have been story telling devices for a long time. Just because story is it's main pull doesn't mean it isn't a game.
I'm up to Episode 3 at the moment and loving it but the one thing I don't like is how linear it is.
It's like a choose your own adventure (story is a tree) except every branch bends back around and grows into the same trunk after a short period. I understand why the developers did it (creating a tree would lead to way more possibilities and way more dev time for less story for those that don't replay the game) but it is a pretty big draw back. I'm waiting for a true choose your own adventure game, TWD is just the start of it.