I passed 21,000 words in the first book of 
my new science fiction series yesterday, officially making it a 
"novella" (novellas are traditionally 20-40,000 words long). I am just 
about to write the "climactic" final scenes, so the final length should 
be just under 23,000 words. As I go through my first real edit next, I 
might add a few bits of dialogue here and there, or even a new scene if 
it appears the story needs it, but in the end, the story will top out at
 no more that 25,000 words, so a novella it is.
While comparing 
this story to my first full-length (95,000-word) novel, Cyberdrome, I 
have to say I really prefer shorter works. It's not that I'm lazy; it's 
just that I really prefer to read medium-length stories, especially if 
there are more stories to come in that universe (I have outlined 4 
stories in this series.) Novellas tend to be more concise and to the 
point (i.e. there is no room for rambling dialogue or "filler" chapters 
in a 20,000-word story.) Novellas are also closer to the structure of 
screenplays, which to me is a good thing.
More on the uniqueness of novellas in the link below:
http://www.newyorker.com/online/blogs/books/2012/10/some-notes-on-the-novella.html