Legacy of the Force is a continuation of the Expanded Universe's trend towards becoming “darker and edgier,” which began in earnest with The New Jedi Order. It takes place forty years after Episode IV: A New Hope and kicks off the Legacy era. As a new Galactic Civil War rages between the Corellian system and the New Republic, the Sith rise again.
(Major spoilers ahead!)
The story of Legacy of the Force begins with the Corellian system -- Han Solo's homeworld -- seceding from the Galactic Alliance. This results in the Second Galactic Civil War. This pits the main characters against each other: while the Jedi are on the side of the Galactic Alliance, Han feels loyal to Corellia, and Leia with him.
Against the backdrop of the war, Jacen Solo, Han and Leia's son, rises to power in the Galactic Alliance. Jacen's desire to return peace to the galaxy leads him on a dangerous path to the dark side of the Force -- a journey facilitated by the Sith Lady Lumiya, who was trained by Darth Vader.
When the other Jedi realize what has happened to Jacen -- who now calls himself Darth Caedus -- they must cast aside the bonds of friendship and family to destroy him before he rebuilds a Sith Empire.
Legacy of the Force consists of nine books:
- Betrayal, by Aaron Allston (May 2006)
- Bloodlines, by Karen Traviss (August 2006)
- Tempest, by Troy Denning (November 2006)
- Exile, by Aaron Allston (February 2007)
- Sacrifice, by Karen Traviss (May 2007)
- Inferno, by Troy Denning (August 2007)
- Fury, by Aaron Allston (November 2007)
- Revelation, by Karen Traviss (February 2008)
- Invincible, by Troy Denning (May 2008)
The series as a whole has issues with pacing; Karen Traviss' books in particular seem to drag. The story reaches its main climax in Sacrifice, and afterwards the backdrop of the Civil War is all but forgotten as the characters spend four entire books trying to defeat Jacen. This may not have been an issue if one or two books could have been cut, instead of having exactly three books for each author.
On the other hand, Del Ray seems to have learned a lesson from the New Jedi Order series, whose division into 19 books and more than a dozen authors led to major inconsistencies in pacing and tone. Allston, Traviss, and Denning have different writing styles and the characterization is somewhat inconsistent between the three, but nevertheless the story is much tighter.
Legacy of the Force contains the highest concentration of major character death in any Star Wars series so far, and this seems to be one of the main reasons why fans dislike the series. Expanded Universe authors have a terrible habit of killing off the next generation characters needed to sustain future books: first Anakin Solo in Star by Star (written by Troy Denning, incidentally), and now Jacen.
But I'm not opposed to character death when it's done well, and I think Karen Traviss (in Sacrifice) and Troy Denning (in Invincible) write the deaths of major characters in a convincing and dramatic way. Jacen's death in particular has a great impact because of how Denning contrasts the younger Jacen's character, in quotes from the Young Jedi Knights series, with his new role as Darth Caedus. And the fact that Jacen's fall and death sets off so many interesting future plot points in Fate of the Jedi, Star Wars: Legacy and more stories to come makes it worthwhile for much more than shock value.
It's easy to dismiss the Legacy series as merely a rehash of the Star Wars prequels, just with new characters and more violence. In many ways, this is a fair criticism. On the other hand, Legacy returns to many of the themes of the original Star Wars films which had been lost in the post-Return of the Jedi Expanded Universe.
With the threat of the Emperor and Darth Vader gone, it feels almost as if the Jedi stopped regarding the dark side of the Force as something incredibly powerful and dangerous. Characters used the dark side and returned to the light with few long-term consequences; it became merely a typical phase during Force training, more like Jedi puberty than a transformation to evil. Eventually, in The New Jedi Order, the Jedi conclude that they must access the dark side of the Force as well as the light in order to maintain balance.
Legacy of the Force brutally destroys this new view of the Force, returning the Star Wars story to its roots. Instead of a struggle against some external enemy, the war is part of the endless cycle of conflict: Jedi against Sith, family against each other. It's dark and depressing, certainly; and yet it's a satisfying and exciting development of events and characters in the Star Wars universe.