We have approached canon. If anyone has ever played a Game of Thrones game, they're mostly pretty disappointing. I haven't played the text-based one, but Ascent, Genesis (the RTS one), and Game of Thrones: The Role-Playing Game...... not a great track record, guys.
Yes, telltale games produces some great work-- they do this fun new take on text-based adventures, kind of, where your dialogue options are what's mostly affecting the environment. It's like Zork on steroids! But I think there are reasonable grounds to remain suspicious of anything that falls under both the categories of "Game of Thrones" and "video game".
Well congratulations, Telltale Games' Game of Thrones, you've swayed my heart!
They actually do a wonderful job of telling a story; they practically mimic George R. R. Martin's voice and style while still delivering an entirely unique and original story, and Telltale Games chose the perfect house to follow: House Forrester. It's an insignificant enough house to take creative liberties with what is happening to them starting at the time of "A Storm of Swords" (the 3rd book/season), but a significant enough house that an avid fan would likely recognize the name.
So far, only 2 out of 5 or 6 episodes have been released-- and I've heard that the iPhone port is quite buggy-- but it's been a lot of fun! Highly recommended.
The gamer in me says 6/10. The Game of Thrones fan says 9. As long as you're not looking for a conventional video game, I'd give it a 7.5 overall. Pretty happy!