Screen Writers Guild of America have decided on the best video game writing of last year:  

VIDEOGAME WRITING WINNER

Uncharted 2: Among Thieves, Written by Amy Hennig; Sony Computer Entertainment

http://www.wga.org/awards/awardssub.aspx?id=1517     
 
And a reminder of those nominations again:  
 

• Assassin's Creed II, Story by Corey May, Script Writers Corey May, Joshua Rubin, Jeffrey Yohalem; Ubisoft Entertainment 
  
• Call of Duty: Modern Warfare 2, Written by Jesse Stern, Additional Writing Steve Fukuda, Story by Todd Alderman, Steve Fukuda, Mackey McCandlish, Zied Rieke, Jesse Stern, Jason West, Battlechatter Dialogue, Sean Slayback; Activision 
  
• Uncharted 2: Among Thieves, Written by Amy Hennig; Sony Computer Entertainment
  
• Wet, Written by Duppy Demetrius; Bethesda Softworks 
  
• X-Men Origins: Wolverine, Script Writer Marc Guggenheim; Activision    
  

[Edited to add: Yay!  I spun this post off in to an acknowledged tip in Joystiq]