A hundred years after the Battle of Yavin, the New Republic is ash, crushed by a resurgent Galactic Empire and it's Sith allies-turned-usurpers. Darth Krayt sits upon the throne, maintaining his power by forsaking the Rule of Two and anointing a half-dozen Sith Lords. A ragtag fleet of Republic ships thwarts his will, as does the Roan Fel, the deposed emperor who resists the Sith from the Imperial home world of Bastion. The Jedi Order is once again decimated, having been all but slaughtered in surprise attacks on their temples on Coruscant and Ossus.
This is the stage for the Star Wars: Legacy Era Campaign Guide, which details the future galaxy as detailed in the Dark Horse comic books of the same name. Wizards of the Coast took a risk releasing a source book with only a comic book series as its inspiration, but it's a gamble that paid off. Though it may be a storyline that only diehard Star Wars Expanded Universe fans are aware of, the _Legacy Era Campaign Guid_e provides a useful sandbox-style campaign setting for Saga Edition where anything is possible.
Literal and figurative ghosts haunt the Legacy Era. The resurgent empire led by Roan Fel seeks to atone for the sins of its past while bringing order to the galaxy while the ghost of Luke Skywalker appears before his last living descendant, the bounty hunter Cade Skywalker and tries get him to accept his destiny. The campaign guide's "Legacy Destiny" mechanic captures these ghosts, allowing players to easily craft connections to Star Wars' deep history. When a legacy is taken, the hero chooses to embrace or deny it. The hero then gets bonuses when working toward the path he chooses, and penalties for working against it. Each of the two dozen legacies also lets players spend destiny points in some unique way; e.g. Skywalkers can spend one to get an instant 20 on a Use the Force skill check
The Legacy Era is a hodgepodge of everything that's come before, and the book reflects that. Its faction-specific chapters for the Galactic Alliance, the Galactic Empire, and the Fringe incorporate all manner of hacked together ships, equipment, and organizations. Most of the new vessels in the book can track their evolution back to some Clone Wars or Rebellion era vehicle, providing the Legacy time period with its own versions of the X-Wing or YT transports. In some cases, the ships themselves are ancient wrecks from those time periods, kept running through upgrades and endless system tweaks.
The faction chapters illustrate how similar – and different – the Legacy era is. The Galactic Alliance isn't the Rebellion, with sympathizers on a thousand worlds. Instead it's little more than a fleet of starships, albeit a very large one. It's evocative of Battlestar Galactica's ragtag fleet of refuges, and it changes the tenor of the organization. The chapter introduces specialized squadrons designed for supply reads, mobile space docks, and space marines trained in ship-to-ship combat. Darth Krayt's Galactic Empire shares the same structure as the familiar one from the Rebellion Era, and much of the same equipment (stormtroopers, imperial walkers, Star Destroyers) but its ruled by a host of Sith Lords, far more than we've seen in any other era.
Technology-wise, the Legacy Era introduces one major disruptive element: Yuuzhan Vong biotech. While the Legacy era takes place a hundred years after the alien, Force-immune Yuuzhan Vong invaded the galaxy, their technology remains potent and accessible. The biggest differences from standard technology and biotech are that they're repaired using "Treat Injury" instead of mechanics, they're difficult to detect or manipulate with the Force, and knowledge checks to determine what they do are based on "life sciences" instead of "technology". The rules introduce a new Biotech Specialist feat that allows heroes to add biotech to existing hardware, as well as new skill rules for manipulating and repairing biotech devices. Biotech is a lightweight, compartmentalized addition to the rules, and they're easy to ignore for those who simply don't like the Yuuzhan Vong.
That said, if you want to run with them, you can. Yuuzhan Vong are one of eight new player species in the Legacy Era. The Vong are mechanically interesting; they're immune to the Force (Will-based Force attacks can affect them), they can never make Use the Force checks, and they don't gain Force points. This makes the Yuuzhan Vong useful as anti-Jedi villains, but I can see them being a challenge for players, particularly when coupled with the fact that most people in the galaxy hate them.
Other notable species include the Chagrian (a amphibious horned species that make for good diplomats), the blue-skinned, red-eyed Chiss (whose most notable member was Grand Admiral Thrawn in the Dark Force Rising trilogy) and the four-armed Codru-Ji (who've made an art of kidnapping, and have children that look like large dogs).
The book two new prestige classes. The first is the Imperial Knight, representing the lightsaber wielding, armor wearing protectors of the Emperor-in-Exile. They are a compromise between the Light-side Jedi and Dark-side Sith, and their prestige class grants access to two new talent trees: Knight's Armor and Knight's Resolve. The Knight's Armor tree provides armor mastery talents typically associated with the soldier, as well as the "Cortosis defense" talent that lets them use specialized gauntlets to block ligthsabers. The "Knight's Resolve" tree grants a number of combat and morale-based talents for bolstering their presence on the front lines.
The second prestige class is the Shaper, which focuses on manipulating biotechnology. Its Implant Talent Tree allows shapers to inject temporary bioimplants into companions, providing temporary boons including extra hit points, attack bonuses, and extra speed. Each one shares the same significant drawback: at the end of the encounter those who receive an implant drop three persistent steps down the condition track. The Shaper's namesake "Shaper" talent tree is focused on manipulating biotech, offering "Biotech Master" (which reduces the amount of time it takes to make a modification), "Expedite Mending" (which offers faster healing of biotech devices) and "Expert Shaper" (which lets them re-roll Treat Injury checks to repair biotech).
The Force Powers section introduces several deadly new powers, which is keeping with the Sith-dominated era, but which GMs might want to think twice about giving to players. The Detonate power causes unattended objects to explode, doing damage to anyone nearby. Lightning Burst is similar to Force Lightning, but works with a burst effect. There are also a few benevolent powers, such as "Enlighten", which allows a Jedi to substitute their Use the Force check for an ally's attack, skill, or opposed check while "Force Shield" erects a telekinetic barrier to protect them from attack.
The Legacy Era Campaign Guide isn't for everyone. It's easy to see how some might object to its kitchen sink-like inclusion of every major theme, hero, villain and technology in the Star Wars universe. Others will find it a welcome sandbox that can include anything but doesn't have to include everything. While there are no "must have" game mechanics like The Clone Wars Campaign Guide's mass combat system, the book's hodgepodge nature means its just as easy to pick stuff for inclusion in other eras (such as introducing legacies to Knights of the Old Republic) as it is to bring ideas from older eras forward.