I'd say time-frame is definately important. If we only get one or two western fantasy shows since the 80s (He-Man, W.I.T.C.H.) then you can't say it's overdone; especially when a lot of those 80s shows were...forgetable, to say the least. The only type of fantasy I might say is overplayed these days is Asian mythology, considering the glut of recent shows that involve it (Jackie Chan Adventures, Xiaolin Showdown, Ninja Turtles, Samurai Jack, Avatar, Jake Long to a degree, and so forth) but as for western-esque fantasy, it's definately a rarity; especially ones that are actually good and put effort into building their world. We got a ton of the Asian-esque shows in a few years, but what was the fantasy show before WITCH? He-Man quite a few years earlier. Before that? Er... I don't recall.