I'm a huge Bujold fan, and Mirror Dance is the start of the superb four-book sequence of the Vorkosigan series that continues with Memory, Komarr and A Civil Campaign. I had forgotten just how much I liked it. It's a tale of redemption, of Mark, the lost clone twin, discovering his own place in the universe rather than being defined as Miles' double; it's a tale of resurrection, Miles himself dying and being brought back to life; and it's a tale of unorthodox families, Mark's relationship with the Vorkosigans of Barrayar contrasting with the corrupt and brutal dynasties of Jackson's Whole, with the Durona clones caught in the middle. It's the first book apart from Ethan of Athos in the series which is not largely told from the viewpoint of Miles or his mother, but from the point of view of a character who has previously been defined by their relationship with Miles. But also Bujold uses Mark to show us Miles's flaws in a way she had not previously done: her unlikely hero has a dark side as well, and Mark both resembles him and differs from him. It's an excellent book and I think might even be a good one to recommend to newcomers to the Vorkosigan universe.
(Only two more Hugo winners to go.)