As was stated the entire game is free - for the weekend only. After that, if you don't purchase it for $9.99, will become unplayable.
Also, for $19.99 you can get:
Unreal Gold
Unreal 2: The Awakening
Unreal Tournament: Game of the Year Edition
Unreal Tournament 2004: Editor's Choice Edition
Unreal Tournament 3: Black Edition
Currently Playing:
Resistance 2 Co-op (anyone call for a Medic?)
Call of Duty: Modern Warfare 2 (PC)
F.E.A.R. (PC)
Currently Ignoring:
My 360 and Wii.