Short version: The game will be 3CD's, include "over 35" (which probably means 36) levels, more gameplay types, mutators and player models. A linux client and server version is included in the box. Also included: Maya Personal Learning Edition, Karma Physics Authoring Tool, UPaint, UnrealEdit 3.0, UnrealScript debugger, and a Karma-vehicle tutorial for modmakers.

A free server for those that want to run a server but not buy the game is coming soon too.

Also, Epic's Steve Polge made a forum post with a partial list of changes made to the game based on demo feedback. Go here for the full map list.