There are other books and short stories in the Mirror Universe
sequence, but you can certainly read Sorrows
and get a complete self-contained story.
The other key works under the Mirror Universe
banner and continuity are the anthologies Glass Empires
and Obsidian Alliances
(with three short novels each, the first one including the original, shorter version of Sorrows
), the short-story anthology Shards and Shadows
(which I have a story in), and the novel Rise Like Lions
by David Mack, which brings the whole saga to a conclusion. The Deep Space Nine
novels Olympus Descending, Warpath, Fearful Symmetry
, and The Soul Key
contain a Mirror Universe arc that feeds into Rise Like Lions
, but as always, the different subseries are designed to be comprehensible on their own and the interconnections are just a bonus.
There are various other MU tales that have been published over the years, including TNG: Dark Mirror
and the Dark Passions
duology, but they're in different continuities from the sequence mentioned above.