I'm also working my way through this one too. It's actually more of an expansion of the original rather than a new game in it's own right. The graphics are more or less the same as the original and apart from a couple of new gadgets and a half dozen new moves everything is much as the first installment. The only reason I can see for releasing it as a new game was the brilliant multiplayer addon.
That being said the original game was great and so to is the sequel. More terrorist new world order nonsense gives Sam Fisher another outing. What makes this game better than the original though is that a lot more thought and effort has gone into the level design. There are some nice new environments to play in (including a speeding train) and some neat touches as you progress along.
However the real joy to this game is the excellent multiplayer. Basically you get to be either a spy or a merc. The spies sneak about trying to steal/blow up stuff and the mercs try to hunt them down. Spys played in 3rd person view can climb and use all the vision modes etc. that Sam Fisher uses in the single player game. The mercs played in 1st person use flash lights and basic motion detectors to try to hunt the spies down. Similar to AvP multiplayer it's a really nailbiting game, especially for the mercs. I doubt it will have real long term appeal but it should be fun for a few weeks (if you can find a free server).
8/10
Splinter Cell MP is just too damn cool for words...
/me sneaks up behind smilodon and breaks his neck