The only thing I've found to be over-done in furry literature is carelessly written, unskillfully rendered story-telling. When a story is well thought-out, spelled correctly, and contains fully-developed, original characters, even the most cliched premise can be made into something compelling and entertaining. I've seen smut with the same-old stories a million times, but when it's well written and skillfully executed, it suddenly becomes interesting again- as if I've never read about "the jock who fell in love with the bookworm in highschool". And at the same time, I've seen a million stories about completely new characters, plots and ideas, in imaginative and unfamiliar worlds- that were so poorly written, that I just couldn't even begin to give a crap about what was going on. Maybe it was a good story- maybe not- but the fact that the plot was something no one had ever done before did nothing to make up for how thoughtlessly it was thrown onto paper. Do you see what I'm saying? I say, if you know you're a good writer, then you can probably make even the most over-done concepts come out as fresh, and interesting.
And for that matter, I actually haven't read a whole lot of human vs. furry stories.
