Not sure why its taken me this long to have a go at it but I sat down with my Son this afternoon to play the Betrayal at Calth board game. We got through the first two scenarios and I found it to be a really easy game to pick up (even for a 7 year old) and a lot of fun to play. Definitely a good way to spend a rainy afternoon inside. The only complication of course was that I painted all of my BoC models as Word Bearers, because you know Ultrasmurfs are loyalist scum after all.
If you have the game and haven't tried it yet then give it go its well worth it - check out the official game play video here.