As mentioned, the campaign is short but fun and very well written. If you ever played the old Shadowrun games or the pen & paper RPG you'll find the dialog to be very immersive and well done.
They're fairly generous with Karma, so you get to try out quite a few different abilities by the time you finish the game, and you can build pretty much any of the basic archetypes: Street Samurai, Rigger, Decker, Mage, Shaman, Physical Adept. Decking is a little lackluster, but does give you access to a few locked areas and they gave them some skills to use in physical combat as well, so you don't feel useless.
I still haven't gotten around to trying any of the downloadable stuff.