Honestly this book felt like such a special treat, just being able to peer into the AGGGTM world again, and see inside Pip's head. I know this takes place before the main series, but I don't recommend reading it until after you read the trilogy. I think it gives you a lot of insight and more hints to the characters that are better appreciated after reading the main story. 
It was short, fun, and showed just how quickly Pip becomes obsessed with even a seemingly simple fun game. It is a testament to Holly Jackson's talents that she is able to make a murder mystery party so tense and have my heart racing! Whenever an author adds a novella or a special epilogue, I always feel like they really loved their story and miss the characters as much as we did. 
If you read the series then I highly recommend this, if just for a happier ending then the main story had.