Just a couple of things about Harn:
A lot of people seem to be under the impression that Harn (i.e., the setting, HarnWorld) is intended for those who want "realism". I don't personally think that's true; Harn is very much a fantasy setting and it's well-suited to those who want to run a "fantasy" game. That said, Harn is more consistent than many other fantasy settings that I've seen. By that, I simply mean that things in Harn make sense: its cultures, its history, the settlement patterns of its inhabitants, etc. -- all of this things are logical. That doesn't mean that they're realistic (although, insofar as Harn is based on medieval Britain, it is quite historically accurate); it just means that the authors have created a fantasy world in a logical way. For me, as a GM, this is great. It gives me a solid foundation upon which I can build my own extensions to the world. Furthermore, it makes for great roleplaying, because the consistency makes it much easier to suspend disbelief and really immerse yourself in the game.
Keith