no its not an extension!!!!
its a new game and from how far ive played , this one is wayyy better than the prequels VANILLA MODE
CLEAR SKY WAS SHIT!
while SOC was a dream come true , but htis one has repairs, better upgrade tree, sleeping, blowouts, nice areas, big guns, and a shitload of crap!
BTW you can order guns now, say you order an Exoskeleton from the special trader, 3-4 days later you get it , but you pay more, better thing is its in prime condition, so no more top of the line suits and guns from the supply traders!
and btw there is a shitload of new items inside!
EDIT: DOWNSIDE IS ITS RUSSIAN ONLY TILL Q1 2010 , and the russian release is set 2nd October!
but fear not! there is a shitty translation that i edited a little so its better!