This is a big box expansion for Arkham horror which adds a second smaller board depicting the Dunwich location. It also adds several new decks as well as adding to the existing ones.
It also adds several new and very interesting characters as well as new ancient ones to tackle. This new expansion tweaks some existing rules and adds new adaptions and challenges.
Having now played this I am very impressed with how this integrates with the main game and it does make a noticeable change to the game. We found that the challenge was significantly ramped up which helps make the game more interesting.
The quality of the pieces are excellent and they have now replaced the basic plastic stands for your characters with much better clear plastic ones allowing you to see more of the nice artwork.
All in all a very worthwhile addition to the game. We did not encounter all the changes in our first play so I will update this review after subsequent plays but I can only see it getting better.