Sci-Fi: Too many space operas. Star Wars was cool, but there are other plot lines. No need for an "evil empire" vs. the righteous minority stories that get get pumped out like their being assembled in a factory. I recently read a book called "Calculating God" about an alien that comes to Earth and spends a lot of time with a human scientist trying to convince him that it's scientifically impossible for god not to exist. Now, I'm an atheist, but what an original and clever idea! We need more writers with ideas like that.
Fantasy: Does every fantasy story HAVE to have elves, dwarves, orcs, and goblins with new names? I love Lord Of the Rings, but copying it and recopying it with different names is really unoriginal. The Eragon series is really popular, and I can't figure out for the life of me why. It reads like a movie script written by a 14 year old. Incidentally it was, yet it's a best seller. I don't get it.
@Jillian: I agree. It started when Anne Rice humanized vampires (though I have to admit, I love her books), but it led to Twilight which aggravates me to no end. They ruined a perfectly good monster and turned it into a bleeding heart teenage angst symbol. What a waste. Though I did recently read a vampire book that was a very interesting take on the subject called "The Passage" by Justin Cronin. I HIGHLY recommend the book, it was truly outstanding. Here is Stephen King's review: Read fifteen pages and you will find yourself captivated; read thirty and you will find yourself taken prisoner and reading late into the night. It has the vividness that only epic works of fantasy and imagination can achieve.