Shadowrun: Sixth World Companion, is a long-awaited book, with the rules for alternate character building systems, meta variants and infected characters, optional and clarified rules, changelings, new qualities and more. It is a needed book but it could have been better with some odd missteps along the way. Even more so than most core books, Games Masters will probably want this just for the optional rules, which address many of the concerns that people have had with the new edition of the rules and players will want it for the wealth of new character options.
Shadowrun: Sixth World Companion is a core character book. It is designed to provide new general options for character building and development. Note this is a long review and you can just take the summary above or if you feel you are interested in my detailed critique, read on.