They have a completely new engine.
It can render the vegetation of those islands better.
There is also a dynamic lighting system that is quite similar to HL2's approach.
And they licensed Havok2, too.
The demo should be out at the end of this month, can't wait :E
Like MrD said, a preloaded but not yet unlocked *.gcf is encrypted with a 128bit key.
You won't ever get that decrypted before it's unlocked...
But after it's unlocked you can simple unpack the *.gcf.
A new video showing a Vampire 2 Demonstration was released today.
http://gamesdomain.yahoo.com/feature/30610
Very cool stuff, they also show off cool VGUI2 possibilities (while hacking the pc).
The remaining parts of the presentation will be made available in the following days...
The HL2's MP will be simple Deathmatch using maps inspired by parts of the Singleplayer.
I am totally sure about that because everything else would be stupid... sorry
Also, there will never be vehicles in CS:S, Valve ment that ground and even
air vehicles are possible with their multiplayer...