Connie Willis writes science fiction, and does a very good job at it. I haven't read all the books that she's written, but I have read quite a few, and a lot of her short stories as well. Her stories are always well-crafted, with interesting characters and plot lines. The dialogue is realistic, and the science is... well, it's science fiction, so that just about sums it up.
She tends to write a lot of stories about time travel, particularly back to the Victorian age. Her novel "To Say Nothing of the Dog" was on that topic, and similarly, the Hugo and Nebula winning "Doomsday Book" was also about time travel, although this time, she went back to the 14th century, in plague-ridden England. Both books won awards and are very good. I enjoy reading them over and over.
Her stories are also humorous; she manages to combine time travel, science fiction, comedy and reality all into one plot.
So if you're looking for a good time travel novel, or an interesting short story, in the science fiction genre, Connie Willis is a good author to start with!