[Varyon]

I feel most settings can be adapted fairly well to most systems, but it can take a lot of work if you're trying to maintain the "feel" of it. In DnD, a single 10th-level Fighter can wade through a small army of goblins with relative impunity, just needing to chug a potion or two afterwards for the lucky hits that got through. In DF, a roughly-comparable [250] Knight who tries that without sound tactics (primarily to keep the goblins from getting behind him/her) is probably down within a few seconds, and dead shortly thereafter, thanks to getting stabbed in the kidneys from behind (or if his armor is too good for that, some stabs to the back of the knee followed by a dagger through the eyeslit). So, if a setting is one that is designed with the expectation that mid-level adventurers can pull such feats off, either your "mid-level" adventurers need some additional points for superpowers in GURPS, or you have to adjust that part of the setting. Even ignoring the self-awareness of the characters from Order of the Stick, DnD or Pathfinder is going to match the feel of their setting better than GURPS DF would. On the other hand, another DnD-inspired setting, Goblin Slayer, would probably have its feel matched better by GURPS DF than by running it in DnD or Pathfinder.