aramis erak
Legend
Seconded.Castles & Crusades SIEGE Engine. Just a regular d20+bonus vs a DC standard D20 system would work better, IMO.
It's even more opaque when you're not a Cthulhu fan. I tried to read the setting info because a friend needed help grasping it... and it felt like word salad... no, not word salad, Voynichese. Clearly linguistic, but making no sense. It was, unlike the Voynich ms., eventually parseable...Cthulhutech: Again, the backstory is a problem. There's a lot of it up-front that you seem to need basic comprehension of to understand the setting, but I couldn't get it straight.
Another where the setting is part of the hangup: Mechanical Dream. The "cool «bleep»" setting elements are some form of miasma that renders much of the world inaccessible at night. The edition I have is a "double book" format (first book is face up, second is upside down and face down; flip along text line axis to make second book face up and upright, with first now face down and upside down. So, literally, no back covers.) A later PDF is clearer, but the setting is still very unclear to me after reading another edition. (JJS, if you're reading this, I still can't grasp it.) It's one of the few where I couldn't get a clear enough mental image to play, let alone run, it. (There are a bunch where I grasp it, but don't want to run them.)
I think most setting first games suffer from this effect. Cases in point include Skyrealms of Jorune, Star Riders (the sequel to Teenagers from Outer Space), Ninja Burger, Coriolis: The Third Horizon, Coriolis: The Great Dark, almost all licensed games...
I found I lacked a lot of mythic context for the monsters in Dragon Warriors. The britanoceltic mythic landscape was something I learned partially from Pendragon.
I find Pendragon is one of the few setting-first games that has enough penetration of the underlying myth, and the myth being so varied, that it's widely acceptable for many - but I have had a few players who needed cuing in to grasp it, as they lacked a cultural context for not just the monsters, but the entire Arthurian myth.


