Beyond the Wall: Further Afield is a supplement for Beyond the Wall and Other Adventures, and I am going to level with you: I don't own the Beyond the Wall, I just bought the expansion, Further Afield.
Why? I read the preview about the shared sandbox tools, and immediately decided that this was worth a purchase. I was not disappointed.
Sandbox tools
The first 15 pages brilliantly layout how to build a "shared" sandbox with your players. At the end of our last D&D session, I decided to see how those rules would play out. Within 45 minutes, we had filled a map full of interesting ruins, surprises, and adventure. The players enjoyed partially building the world, and all of them had great ideas for locations and embellishments to add. I left the table inspired.
I know there are issues allowing players to participate in world creation as it ruins the surprise. To allay these concerns, the game includes a mechanic to test the truth of what the players created. Not every rumor heard in a bar is true, and not all that glitters is gold. Based on what we all rolled, I am sure the players will be very surprised.
A pleasant side effect of this collaborative building, is that the players have some of the in game knowledge that their characters would have, all without reading 27 pages of back story.
Threats
The game uses "threats" to track the players' primary adversaries. I haven't used or built a threat, but the concept is interesting. It feels close to something like a Front in Dungeon World, although I have never used either in a game. I feel that for the prep-light games I run, synthesizing the main antagonist down in this fashion is useful. I am excited to use the concept during my current D&D campaign.
Other stuff:
About half the book is additional material for a game I don't own. Oops.
Bottom Line:
I don't own Beyond the Wall, but Further Afield was worth the purchase. The sandbox creation rules are worth the $6 price of admission.