I'm not a huge Soundgarden fan, yet, but I own this, Badmotorfinger and Superunknown. This compilation is great for those that have not heard much Soundgarden, and possibly the best grunge related compilation for your money.
Songs like Jesus Christ Pose and Outshined have a heavy crunch unique to Soundgarden while Blow Up the Outside World and Pretty Noose are surprisingly melodic and give as show us a different side to the band. The Highlights for me though are Loud Love and Nothing to Say. These earlier cuts have a rawer feel and are enough for me to look into Soundgarden's earlier albums. The riff to Loud Love is fantastic and Nothing to Say is a landmark grunge song.
All in all, great riffs, great vocals and for a fiver, this is a great place to start.