its still the same stalker, BUT with many improvements and a new story
the most important part of stalker is imo the atmosphere, well in CS its even better: we have finally 'clear' sky, i mean there is sun and we can see not only grey clouds and the night is really dark and scary (i know there were some weather mods for SOC but ill talk about the 'default' game)
my favorite scene was a firefight between the army and stalkers during night in the second location, i was so impressed that i was watching it without making anything and failed the quest to rescue this stalkers
the so called a-life, which was pretty poorly done in SOC is now really good with all this 'gang-wars', and it really feels like a war when you have to take over villages, farms, watchtowers and all the stuff that makes a good cp with your mates, that dont just run into the action and die
and you can (FINALLY
) repair your weapons and armor, moreover you can upgrade it to make it more powerful, accurate.... well you can make a killing machine using an AK-74u, however its pretty expensivenew loaction like swamps or forest (the locations in SOC were kinda similar, only pripyat was different)
the graphics are also better, but its still not so good as crysis (but crysis has got only good graphic and nothing else)
ok, what i want to say by writing all that stuff is that if you like SOC, or just good shooters with scary atmosphere (just remember secret underground facilities in SOC) you should try it out, its really worth it
)
now that is quite a pile of money 
oh i now what is changed i can't KILL anybody without spending 3 orange med pack's because the aim has changed and it is lower now that reallyyyyyyyyyyyyyyyyyyyyyyyyyyyy stinks 
