As a disclaimer, I received a free copy of the book in exchange for helping review it and provide feedback. I have not yet played/ran it, so this review is based on a thorough reading of  it. 

Ruins of the Rustworm is a fantastic, evocative adventure with multiple fun and distinct factions, a huge map to explore, and enough cool descriptions that I started planning out a game whilst reviewing my copy. 

It manages to be properly system-agnostic, unlike many other claimants. Instead of providing stat blocks for creatures, they are given strong descriptions of their advantages and drawbacks, and general tactics, which look to be easily adapted to other systems as long as you have a reasonable grasp of said system. 

I took a random monster and was able to stat up a reasonable Heart version of it in about two minutes, in an encounter that felt like it'd be very fun - hit and run ambushes in a lava pit. 

Various event and encounter tables are provided, generally with loose mechanics that should be easily adaptable to most tables (e.g. "The floor is brittle and may fall out from under you. DEX Save to avoid falling"). 

The zine is highly focused on dungeon delving, and relatively low on social aspects but does include a few interesting opportunities for them. It feels like it's best suited to a relatively low-magic game, due to the high number of environmental hazards, but a high-magic system at lower levels would also likelywork fine.

All in all, highly looking forward to running it sometime, and I'll update here when I do.