Yes, I've played the demo version of Portal.
Every single item in L4D2 is available!
In-game difficulty selection.
I simply love the slow-mo during explosions.
Cons:
Sometimes, NPC survivors won't go through the difficulty door I picked, changing the game's difficulty... (Or, at least, I think it does, considering I can't get bronze on my own at easy.)
Pros:
Cons:
Conclusion:
This review was posted before the latest release.