Let me google that for you:

http://www.google.com/search?q=witcher+2+2.0

http://www.eurogamer.net/articles/2011-08-17-witcher-2-2-0-update-adds-dark-mode

http://www.videogamer.com/pc/the_witcher_2/news/cd_projekt_details_witcher_2_2_0_update.html

"the free update brings with it technical enhancements, gameplay tweaks and major new features."

"The biggest new features are Dark Mode and Arena. Dark Mode is a new difficulty setting that ups the challenge and adds a number of powerful 'Dark' items. Arena mode is just what you think it is, pitting you against endless waves of enemies while you pick up vital XP."

"A new tutorial has also been added in order to help beginners through the early stages of the game."

http://www.google.com/search?q=witcher+2+2.0

http://www.eurogamer.net/articles/2011-08-17-witcher-2-2-0-update-adds-dark-mode

http://www.videogamer.com/pc/the_witcher_2/news/cd_projekt_details_witcher_2_2_0_update.html

"the free update brings with it technical enhancements, gameplay tweaks and major new features."

"The biggest new features are Dark Mode and Arena. Dark Mode is a new difficulty setting that ups the challenge and adds a number of powerful 'Dark' items. Arena mode is just what you think it is, pitting you against endless waves of enemies while you pick up vital XP."

"A new tutorial has also been added in order to help beginners through the early stages of the game."