Finally, a thread I've been waiting for.
Anyway, it's not even all of those little things you mentioned that make it revolutionary. It's more than that; other games have told dark and mature stories but it's the way it was implemented that made it something special. It uses the gameplay and your choices to reiterate the themes of said narrative, and uses it to come to a satisfyingly yet horrifying and emotional resolution that truly drives the message home.
Silent Hill 2 came close, but it was missing that special link between the player and James Sunderland that Telltale was able to make work with Lee and the player, and most of that was due to how they used Clementine and Lee. It didn't do much for gameplay itself, but for interactive storytelling, Telltale has transcended gaming and what kind of stories it is able to tell, which can now rival any classic novel.
If you want to know more about what I think, I created a thread with
my thoughts here a little while ago, where I touch upon the aspects I liked and thought were worthy of discussion.