There was a recent forum discussion about fantasy RPG geography peeves. I actually don't worry much about non-realistic geography, but I do object to boring geography. The way I see it, you may have ordinary rivers, lakes, mountains, and woods in your central, civilized areas, but in the adventure-filled wilderness, why add a river to the map if it's just another river? A river of fire, or a river of forgetfulness is more interesting. Or a river that flows straight up into the sky. Or that freezes solid every night and thaws before dawn. And why should a mountain be merely a mountain, when it could be a floating mountain, or mountain that stands on its head, or a mountain of glass? Or a sleeping giant who wakes once a month to move to a new location? Or a perfect cube? Or a normal-looking mountain, but five-foot metal barbs erupt from the ground as adventurers attempt to negotiate the lower slopes? Or a monstrous eye opens, spying on the travelers?
What really bothers me is when I read fantasy maps or gazetteers and there are fantastic-sounding names, like The River of Blood, but it turns out it's just a mundane river reddened by silt. Or a Sea of Glass that's not actually glass, or contains no glass, and doesn't even have a legend of turning to glass at some point in the past. It's false advertising: "Here are a few place-names that sound interesting, but really that's as far as it goes. This product actually contains pages and pages of mundane geography descriptions."