And first up in the Nebula Novella category, it's The Man Who Bridged the Mist, by Kij Johnson. I generally like her work, and there's nothing not to like here. But it's hard to say why this is nominated, because it's pretty obviously not a standalone story. Kij Johnson has generally worked in shorter forms--the intro to the story says this is a venture into longer work. But this is a sketch of at least a novel, and she is most likely hoping it could be a series. It sets out a landscape ripe for storymaking. There's an unusual environmental challenge in the Mist, a weird caustic semi-solid that fills some major canyons on this world. There are life forms small and big in it, so plenty of room for interesting biology and nature challenge. There are families of ferrymen who seem to have a supernatural "feel" for how and when to cross it. And we have Kit Meinem, an engineer/architect at a time when the people are just becoming technologically sophisticated enough to build bridges over this mist. This is the story of Kit's attempt to bridge the largest chasm. It's well told, but there's no particular plot tension. It just lays out the characters and scenes. So it's likely the first chapter or two of a novel. Fine, but not necessarily an award winner on its own. I give it 3 stars and look forward to the novel.
I had to come back and edit this post, as I somehow missed the fact that the link to the Asimov's version of the story was part 1 of 2, and part 2 was not free. Kij Johnson has posted the entire story on her website at the above link.
Once I read the whole thing, it is indeed a complete story. I still think the above comments are correct. It makes a good precursor for a world of stories. This one went on to win the Hugo for 2011. I am not sure that I completely agree, but can live with it. It's a very interesting "big plan" engineering story, but does not have the excruciating (and/or fascinating) technical detail of some stories of this kind. The protagonist is a fairly cool character, so though he does in the end form a romantic attachment it doesn't really tear at you. It is a measured work. Go read the whole thing, now that I've found it all.