Having played through the demo a few times now... Single player only, I have a thoughts.
-The AI director does a great job of mixing up the action, keeping it fresh
-I am sure that when the mod community gets a hold of this, the mods will be awesome!
-The team mate AI is decent, they will save your butt from time to time
-Frame rates are great due to a good looking but older engine.
-Inability to am down iron sights. Yes you have scoped on certain weapons, but come on... Seriously?
-The team mate AI is decent, they will let you die from time to time
-I am using Vista Ultimate x64 and I have had 1 crash to desktop and on almost(frozen screen and looping sound), but it pulled out of the latter.
I would love to try out the multiplayer and see how playing wit other people in real life will playout.
Definitely try out the demo when it becomes available to you, or buy it if you love shooting zombies.