You'll get three new race types - Eliminator, Zone Battle and Detonator along with 12 new tracks, 13 news ships, 6 new music tracks, redesigned menu system, new campaign, new trophies and new online ranks to achieve.
Eliminator is a modified version of Wipeout Pulse that allows you to flip your ship, fly backwards and shoot oncoming opponents. They also modified the point system so that you get points for completing laps, inflicting damage and kills.
Zone Battle is an 8 player version of the Zone mode.
Oddly, no details on the Detonator mode.
Still, pretty good amount of content for the price. Especially since Wipeout HD is now on sale in the PSN store for $14.99.
The Patch on the 21st will add new features and tweaks like a statistics section, redesigned ship and track selection screens and new community/online features.