Beat this yesterday. I have mixed feelings about it. I think many of the fire fights are better than the original, there are some massive shoot outs, but there is very little new here, and the expansion was missing some things that made the original good.
There is very little variety here, much like the original, but with an expansion I wish they had brought some bigger changes. There were some new weapons and a couple new enemies, but I couldn't stand the invisible ghosts.
To me the expansion didn't have the pacing and story to keep you intersted like the original. I guess I never realized how much I enjoyed the characters in the original, especially the nerdy computer guy who kept screwing you over. Also the entire plot line in this is literally, get to the extraction point.
But the AI is still amazing and I think I found this one a little more nerve racking than the original.