So, without spoiling anything, I must say that The Last Of Us is an incredible bit of television. It respects the hell out of the source material while building on it to somehow elevate it even further.
All the main plot points seem to match the game, but we get to see much more of parts that were just brief flashbacks in the game, or hinted at with notes.
Bill's episode, in particular, is a marvelous example of improving on the source material (and the casting!!).