To my tastes, the novelette category consists of four good stories and one great one.
Starting with the good, Paul Cornell's "The Copenhagen Interpretation" is a fun romp through a distinctive alternate history with some interesting speculations. It's the same setting as his prior Hugo nominee "One of Our Bastards Is Missing." Neither story struck me as having the depth I look for in a Hugo winner, but it also doesn't strike me that Cornell was shooting for that. He was just telling an entertaining story, and I can hardly blame him if people responded well enough to put it on the Hugo ballot.
Geoff Ryman's "What We Found" and Rachel Swirsky's "Fields of Gold" each ran into the same unfair problem——the authors have set my expectations unreasonably high. "What We Found" and "Fields of Gold" are both very nicely written, but I couldn't help feeling disappointed that they weren't quite so amazing as "Pol Pot's Beautiful Daughter" or "The Lady Who Plucked Red Flowers Beneath the Queen's Window." Serves them both right for being so bloody good.
"Six Months, Three Days" by Charlie Jane Anders is a very clever piece. I love the interplay between the two main characters, with their two opposing forms of clairvoyance. Even if the romance aspect of the tale didn't pull me in quite as much as I might have liked, it's still a memorable story.
My hands-down choice for best novelette of 2011 (from the day I first read it) is "Ray of Light" by Brad R. Torgersen. (And I'm not saying that just because Brad was so nice to all us new Writers of the Future kids last year.) "Ray of Light" is an engaging story with an emotionally charged ending. At the same time, it's a wonderful counterpoint to the dismal tone of so much of the current science fiction and fantasy field. Brad takes a bleak premise and turns it into an uplifting reading experience. Great work!
Aaron's Ballot for Best Novelette
1. Brad R. Torgersen - Ray of Light
2. Charlie Jane Anders - Six Months, Three Days
3. Rachel Swirsky - Fields of Gold
4. Geoff Ryman - What We Found
5. Paul Cornell - The Copenhagen Interpretation